← Guides

Putting images inside a book

An image that looks sharp on screen is often too coarse to print, and the same picture behaves completely differently in a PDF and an EPUB. Here is how to work out whether yours is good enough, and where it will actually appear.

The Nueel team10 min readUpdated 5 September 2026

Images are where a book most often fails between the screen and the page, and the reason is arithmetic rather than taste. A picture that looks perfectly sharp while you are placing it can be visibly coarse when printed, and nothing in the editing view tells you.

Effective resolution is the only number that matters

An image file has a pixel count. That is fixed. What varies is how large you print it, and the quality you get is the ratio between the two.

effective PPI = pixel width ÷ printed width in inches

A 1500-pixel-wide image:

Printed across Effective PPI Verdict
3″ 500 More than enough
5″ 300 Right at the target
7.5″ 200 Below target; may show less detail
10″ 150 Well under the target

The same file, four different outcomes. This is why “is this image high enough resolution” has no answer until you say how big it will be on the page. If the image has been stretched, check both axes.

The resolution tag stored inside a file is metadata and can say anything: a photograph tagged 72 PPI with 4000 pixels of width is excellent for print at the right size, and one tagged 300 PPI with 500 pixels is not. The real test is pixel dimensions plus final placed size — which is exactly the division above.

The thresholds, and who sets them

  • 300 PPI at final size is the normal target for photographs and continuous-tone greyscale — KDP requires at least 300, and IngramSpark specifies it for interiors.
  • 600 PPI is appropriate for rasterised 1-bit line art — engravings, diagrams with hard edges and no intermediate tones, where stepping along a diagonal shows at 300. Vector artwork should usually stay vector instead.
  • Below 300 PPI an image is below the target and should be flagged for review. KDP describes images under 200 DPI as low resolution; whether a given image at that size looks soft depends on the picture, the paper and the printing.
  • IngramSpark’s interior spec rejects colour images below 72 PPI. Its cover specification is stricter again — images below 200 PPI there may be rejected.

These are per destination, not one universal number: a platform’s preferred resolution and its refusal threshold are different figures, and an image between them prints poorly without being refused. A report that collapses them produces either blocked books the printer would have printed or passed books it will refuse.

You cannot add resolution afterwards

Enlarging an image adds pixels by interpolation: the software guesses what would have been between the pixels you have. The result is larger and softer, never sharper, because the detail was never captured.

“AI upscaling” is the same operation with a better guesser. It can improve apparent sharpness, but it synthesises detail rather than recovering it. For a photograph in a book — particularly a photograph of a real place or person — inventing detail is not a neutral act.

The real fixes are to find a larger original, or to print the image smaller. Both are much easier before a book is laid out than after.

Screens can hide print-resolution problems

A screen preview is not a reliable test of print resolution. Modern displays can exceed 250 pixels per inch — a current iPad is 264 — and a printer’s own DPI is a different measurement entirely, with several printer dots reproducing one image pixel. What matters for the source image is how many image pixels are available for each inch it occupies on the printed page.

A 1500-pixel image displayed at whatever size your editor happens to choose may look perfectly sharp on screen. Printed 5 inches wide it supplies 300 pixels per inch; printed 10 inches wide it supplies 150. Calculate the effective PPI at final size rather than judging by the monitor.

Printing at 100% actual size on an office printer can expose obvious pixelation, but it is a rough check, not a simulation of POD output — the reliable final check is a proof copy.

Images in an EPUB behave differently

The print rules above are about resolution. In a reflowable ebook, the harder problem is placement.

There is no fixed page, so a position composed for print cannot be assumed to survive. EPUB and Kindle can place an image beside text using floats, but the result varies with screen width, font size and reading system. For ordinary illustrations, the most robust choice is a block image in the text flow, above or below the relevant paragraph — Amazon expects the majority of images to be block images, even though float and inline placement are supported. A caption should be structurally attached to its image — a figure containing the image and the caption — but even semantic grouping cannot promise that no reading system will ever paginate between them.

Two other constraints:

  • Pixel ceilings. Several platforms cap the pixels in a single image, because the reading device has to decode it within a fixed memory budget. IngramSpark’s limit is 3.2 million pixels per image; Apple Books allows 5.6 million inside the EPUB. A very large photograph can therefore be refused for being too big — the opposite failure to the print one.
  • File size. Every image ships inside the book file, and total size limits are real.

The practical consequence: print and ebook often benefit from separate assets. The print PDF wants enough resolution for the target size — not the largest file you have, since KDP warns that excessively high-resolution images can cause processing problems — and often CMYK or greyscale; the EPUB wants a screen-sized image in sRGB, which is what Kindle and Apple Books specify.

Alt text is not optional any more

Every image that carries meaning needs a description for readers who cannot see it. Kindle’s and Apple Books’ publishing guidance both instruct publishers to supply alt attributes, and the European Accessibility Act has applied to covered ebook services in the EU since 28 June 2025 — with exemptions, including for microenterprises providing services. Accessibility is now part of the compliance landscape as well as good publishing practice.

Write it for a person, not a search engine:

  • Bad: “Figure 3.2” — describes a file.
  • Bad: “book formatting typesetting image” — describes nothing, to anybody.
  • Good: “A woodcut of a hare running across a ploughed field, with a church tower on the horizon.”

Purely decorative images take an explicitly empty alt attribute, which tells a screen reader to skip them. That is different from having no alt attribute at all — without one, some screen readers fall back to announcing the filename.

Captions

A caption belongs to its image structurally, not spatially. In print they sit together on the page; in an EPUB, they have to be bound together or a page break can separate them.

Captions set smaller than body text, usually a point or two down, and often in a different style altogether. They are not body text and should not read as though the prose has continued.

Before you export

  1. Work out the effective PPI of every image at its printed size, not its file size — 300 for photographs, 600 for rasterised line art, and flag anything below target for review.
  2. Convert to greyscale yourself for a black-and-white interior; to CMYK for colour print; to sRGB for the EPUB.
  3. Give every meaningful image real alt text, and mark decorative ones as decorative.
  4. Attach captions structurally.
  5. Keep the EPUB’s images within the store’s per-image pixel ceiling and the book’s file-size limit.

Almost every image problem in a finished book was fixable at the start and unfixable at the end. The original detail either exists in the source or it does not; processing can interpolate or synthesise, but it cannot recover information that was never captured.

Nueel measures effective resolution from the pixel dimensions and the size the image is actually placed at, so a picture that is fine at three inches and too coarse at seven is reported when it moves rather than when it was imported — and it keeps the thresholds per destination, matching each printer’s own numbers. Images, captions and their alt text are one block in the document, so the caption and the description ship bound to the figure in the EPUB rather than as paragraphs next to it.

Sources

Common questions

What resolution do images need for a printed book?
300 PPI at the size the image is actually printed — the working target for photographs and greyscale. Rasterised 1-bit line art usually wants 600 PPI, though vector diagrams should stay vector. The number that matters is the effective resolution after placement, which is pixel dimensions plus final placed size — not the resolution the file's own metadata reports.
How do I calculate effective PPI?
Divide the image's pixel width by its printed width in inches. A 1500-pixel-wide image printed across 5 inches is 300 PPI; across 7.5 inches it is 200 PPI. If the image has been stretched, check both axes. Enlarging an image in the layout lowers its effective resolution proportionally, which is why a file can be fine in one place and coarse in another.
Can I increase the resolution of an image I already have?
Not in the sense that matters. Enlarging adds pixels by interpolation, and AI upscalers synthesise plausible detail — but neither recovers information that was never captured. For a photograph of a real place or person, invented detail is not a neutral act. The real fixes are a larger original or a smaller placement.
Why does my image look fine on screen but print badly?
Because a screen preview is not a test of print resolution. Modern displays can exceed 250 pixels per inch, and a printer's DPI is a different measurement entirely — several printer dots reproduce one image pixel. What matters is how many image pixels are available for each inch the image occupies on the page. Calculate the effective PPI at final size, or print a proof.
Where do images appear in an ebook?
Mostly between paragraphs, in the flow of the text — that is what Amazon expects for the majority of images. A reflowable ebook has no fixed page, so a print arrangement cannot be assumed to survive; EPUB and Kindle do support floated and inline images, but the result varies with screen width, font size and reading system. Block placement above or below the relevant paragraph is the most robust choice, with captions attached structurally.
Do images in a book need alt text?
Every meaningful image in an accessible ebook needs a text alternative, and Kindle's and Apple's publishing guidance both instruct it. The European Accessibility Act has applied to covered ebook services in the EU since 28 June 2025 — with exemptions, including for microenterprises providing services — so accessibility is part of the compliance landscape as well as good practice. Purely decorative images take an explicitly empty alt attribute.
Should images be RGB or CMYK?
Follow the specification of the destination. Colour print services specify CMYK — IngramSpark caps total ink at 240% — and for a black-and-white interior, convert to greyscale yourself rather than letting the printer do it. Ebooks are the opposite: Kindle and Apple Books want sRGB.

Nueel is a web app that turns a finished manuscript into a typeset book, in your browser: import your Word file, choose a design, export a print-ready PDF and an EPUB. See how it works.