Filename case sensitivity issue?

There was a discussion recently that the image files have to be named with a fully lowercase extension, otherwise they will not be found. Presumably this is on Linux where filenames are case-sensitive. Might be worth checking the file extensions in a case sensitive way

Start by locating the code that discovers or validates image files and inspect how filename extensions are compared. Reproduce the behavior with differently cased extensions on Linux, then add coverage and confirm that supported image files are found consistently regardless of extension case.

Written by the indexing model from the issue text.