What resolution do images need for a printed book?

300 DPI at the size the image is actually printed, which is the working standard for photographs and greyscale. Line art with no intermediate tones usually wants 600. The number that matters is the effective resolution after placement, not the resolution the file reports on its own.

How do I calculate effective DPI?

Divide the image's pixel width by its printed width in inches. A 1500-pixel-wide image printed across 5 inches is 300 DPI. The same image printed across 7.5 inches is 200 DPI. Enlarging an image in the layout lowers its effective resolution proportionally, which is why a file can be fine in one place and too coarse in another.

Can I increase the resolution of an image I already have?

Not meaningfully. Enlarging adds pixels by interpolation, which invents detail that was never captured, and the result looks soft rather than sharp. The only real fixes are to obtain a larger original or to print the image smaller. This is why the resolution question belongs at the start of a project.

Why does my image look fine on screen but print badly?

Because a screen shows perhaps 100 to 160 pixels per inch and a printer lays down 300 or more. An image can have plenty of pixels for the screen you are checking it on and nowhere near enough for the page, and there is no way to see the difference without doing the arithmetic or printing it.

Do images in a book need alt text?

Yes, and it is now a compliance requirement rather than good practice. The European Accessibility Act applies from June 2025 and covers ebooks, so distributors selling into the EU expect it. Write it for a reader who cannot see the image, and mark purely decorative images as decorative, which produces an empty alt attribute rather than none.

Should images be RGB or CMYK?

Follow the specification your printer publishes. Colour print services generally want CMYK, and IngramSpark caps total ink at 240%. For a black-and-white interior, convert to greyscale yourself rather than letting the printer do it, because a conversion you did not control is a conversion you cannot correct.

Putting images inside a book

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 DPI = pixel width ÷ printed width in inches

A 1500-pixel-wide image:

Printed across	Effective DPI	Verdict
3″	500	More than enough
5″	300	Right at the standard
7.5″	200	Visibly soft
10″	150	Poor

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.

Any DPI figure stored inside the file itself is metadata and can say anything. A photograph tagged 72 DPI with 4000 pixels of width is excellent for print; one tagged 300 DPI with 500 pixels is not. Read the pixel dimensions, never the tag.

The thresholds

300 DPI at printed size is the working standard for photographs and greyscale images.
600 DPI is usual for 1-bit line art — diagrams, engravings, anything with hard edges and no intermediate tones, where stepping along a diagonal is obvious at 300.
150 DPI is the floor at which most people can still call a printed image acceptable rather than good.
Below 72 DPI, IngramSpark rejects the file outright.

That last pair is worth separating deliberately. The recommendation and the refusal threshold are different numbers, and an image between them prints poorly without being refused. Collapsing them into one figure produces a report that either blocks books the printer would have printed, or passes 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 invents plausible detail. 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 lie about print

A screen shows roughly 100 to 160 pixels per inch. Print lays down 300 or more.

So an image can be perfectly sharp on the display you are checking it on and have less than half the detail the page requires. Zooming in does not simulate this, because zooming shows you more screen pixels per image pixel — the opposite of what printing does.

The only reliable checks are the arithmetic above, or printing the page on any office printer and looking at it.

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 page, so there is no “beside”. An image anchored next to a paragraph in a print layout becomes an image above or below that paragraph in an EPUB, with the text continuing underneath. A caption has to be structurally attached to its image rather than positioned near it, or the two can be separated by a screen break.

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 stated limit is 3.2 million pixels per image; some other platforms publish higher figures. A very large photograph can therefore be refused for being too big, which is 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 is that print and ebook want different image files: the print PDF wants the largest version you have, and the EPUB wants one sized for a screen.

Alt text is not optional any more

Every image that carries meaning needs a description for readers who cannot see it. The European Accessibility Act applies from June 2025 and covers ebooks, so distributors selling into the EU now expect accessibility metadata, and files without it are increasingly refused.

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, which tells it nothing and leaves it announcing a 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

Work out the effective DPI of every image at its printed size, not its file size.
300 for photographs, 600 for line art. Anything under 150 needs a better original or a smaller placement.
Convert to greyscale yourself for a black-and-white interior; to CMYK for colour print.
Give every meaningful image real alt text, and mark decorative ones as decorative.
Attach captions structurally.
Use screen-sized images for the EPUB, and check any per-image pixel ceiling.

Almost every image problem in a finished book was fixable at the start and unfixable at the end. The pixels either exist or they do not, and no amount of processing changes which.

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. Images, captions and their alt text are one block in the document, which is why the caption cannot be orphaned from its figure in the EPUB and the alt text cannot be lost on the way to it.

Common questions

What resolution do images need for a printed book?: 300 DPI at the size the image is actually printed, which is the working standard for photographs and greyscale. Line art with no intermediate tones usually wants 600. The number that matters is the effective resolution after placement, not the resolution the file reports on its own.
How do I calculate effective DPI?: Divide the image's pixel width by its printed width in inches. A 1500-pixel-wide image printed across 5 inches is 300 DPI. The same image printed across 7.5 inches is 200 DPI. Enlarging an image in the layout lowers its effective resolution proportionally, which is why a file can be fine in one place and too coarse in another.
Can I increase the resolution of an image I already have?: Not meaningfully. Enlarging adds pixels by interpolation, which invents detail that was never captured, and the result looks soft rather than sharp. The only real fixes are to obtain a larger original or to print the image smaller. This is why the resolution question belongs at the start of a project.
Why does my image look fine on screen but print badly?: Because a screen shows perhaps 100 to 160 pixels per inch and a printer lays down 300 or more. An image can have plenty of pixels for the screen you are checking it on and nowhere near enough for the page, and there is no way to see the difference without doing the arithmetic or printing it.
Where do images appear in an ebook?: Between paragraphs, in the flow of the text. A reflowable ebook has no fixed page, so there is no beside for an image to sit at. Anything anchored next to a paragraph in a print layout becomes an image above or below that paragraph in an EPUB, and any caption has to be attached to it structurally rather than positioned near it.
Do images in a book need alt text?: Yes, and it is now a compliance requirement rather than good practice. The European Accessibility Act applies from June 2025 and covers ebooks, so distributors selling into the EU expect it. Write it for a reader who cannot see the image, and mark purely decorative images as decorative, which produces an empty alt attribute rather than none.
Should images be RGB or CMYK?: Follow the specification your printer publishes. Colour print services generally want CMYK, and IngramSpark caps total ink at 240%. For a black-and-white interior, convert to greyscale yourself rather than letting the printer do it, because a conversion you did not control is a conversion you cannot correct.