# MED-003: img in picture not core type, how to fix it

Source: https://epubcc.com/epubcheck/med-003/ (updated 2026-11-04)

EPUBCheck MED-003 is an error message: “Picture "img" elements must reference core media type resources, but found resource "…" of type "…".” An img inside a picture element points to an image in a format that is not a core media type. Inside picture, the img must always reference a core image type (JPEG, PNG, GIF, WebP or SVG) so every reading app can show it; EPUBCheck names the file and its type.

- Official message (EPUBCheck 5.4.0): Picture "img" elements must reference core media type resources, but found resource "%1$s" of type "%2$s".
- Default severity: Error

## Typical causes

- TIFF, BMP, HEIC or other formats that reading apps are not required to display.
- A picture element written for the web, with the modern format in img and the fallback in source.

## How to fix it

1. Convert the image to JPEG, PNG, GIF, WebP or SVG and update the src and the manifest media type.
2. If you want to offer another format, put it in a source element with a type attribute, and keep a core format in the img.
3. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If a source element in the picture lacks a type attribute for a foreign format, that is MED_007.

## Sources

- EPUB 3.3, §3.5.2.2 HTML img fallbacks: https://www.w3.org/TR/epub-33/#sec-fallbacks-img (read 2026-11-04)
- EPUB 3.3, §3.2 Core media types: https://www.w3.org/TR/epub-33/#sec-core-media-types (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.