EPUB Error: Missing Alt Text on Images (ACC-001)
What causes this error?
The EPUB Accessibility specification — aligned with WCAG 2.0 Level AA — requires every <img> element in EPUB content files to carry an alt attribute. This attribute provides a text alternative for readers using screen readers, text-to-speech, or devices that cannot display images. EPUBCheck reports ACC-001 when any image element is missing this attribute entirely. Apple Books has enforced accessibility validation since 2022 and will flag or reject files with ACC-001 errors. Even for decorative images that convey no information, the attribute is still required — it should be present but set to an empty string (alt=""), which signals to assistive technology that the image can be safely ignored. Missing alt text most often appears in EPUBs converted from Word or InDesign exports where images were inserted without document-level alt text set in the source.
How to fix it
- Run EPUBCheck to get a list of all ACC-001 errors — each one includes the chapter file and line number of the
<img>missing an alt attribute. - For each flagged image, decide whether it is a content image (conveys information the reader needs) or a decorative image (purely visual, adds nothing to the reading experience).
- For content images, add a descriptive alt attribute:
<img src="chart.png" alt="Bar chart showing sales by quarter"/>. Describe what the image shows, not what it looks like — focus on the information it communicates. - For decorative images, add an empty alt attribute:
<img src="divider.png" alt=""/>. This tells screen readers to skip the image entirely rather than announcing "image" with no description. - Re-validate with EPUBCheck after updating all chapter files. If submitting to Apple Books, use the Accessibility checker in Calibre (Edit Book → Tools → Check Accessibility) as an additional pass before upload.
Common questions
Do I need alt text even for images that are just decorative chapter dividers?
Yes — the alt attribute is required on every img element regardless of whether the image carries meaning. For purely decorative images, use an empty alt attribute (alt="") rather than omitting it. An empty alt tells assistive technology to skip the image; a missing alt attribute causes a validation error and may cause screen readers to announce the filename instead.
Apple Books accepted my EPUB before — why is it now rejecting on missing alt text?
Apple Books tightened its accessibility validation requirements in 2022 to align with the EPUB Accessibility 1.1 specification. Files that passed upload before this change may no longer pass the current validation. Adding alt text to all images is now a baseline requirement for Apple Books submission.
Check your EPUB before uploading
The free EPUB Validator catches structure, metadata, and navigation errors — no signup, no Java, runs in the browser.
Validate Your EPUB Free →Building your EPUB correctly from the start prevents most of these errors before they happen. See the EPUB formatting guide for the full workflow: manuscript cleanup, TOC, front matter, EPUB 3.0 generation, and validation.
Common EPUB errors: Invalid image format in EPUB, EMF image fallback error
Platform rejection guides: Why Apple Books rejects ebooks