Was creating some QA tests involving creation of contents in mod_book and, no matter the repository I try to pick the image (tried update, local FS files, server files) and the type of the image (tried gif and png), I always end with one of theses messages shown in one dialog:

• image/png filetype cannot be accepted
• Image (PNG) filetype cannot be accepted.

Confirmed both under Safari and Firefox. Also tried it in mod_forum and got same problem, so I bet it's global.

Ciao