SDL_Image useable in software with "non-free" licenses?

It appears, at least to me, that part of the SDL_Image library is licensed under the GNU Library Public license, specifically the png portions of it. To what extent does this prohibit linking, especially (but not exclusively) statically, to SDL_Image with software under custom licenses, and what portions of SDL_Image are covered by it?

Where did you get that impression?
Both SDL_image/LICENSE.txt at main · libsdl-org/SDL_image · GitHub and SDL_image/IMG_png.c at main · libsdl-org/SDL_image · GitHub clearly are zlib license

The source archives at http://www.libsdl.org/projects/SDL_image/ include a license notice in the png source file. I didn’t check the GitHub one, which indeed seems to have been updated. Sorry about the confusion.

Oh, right, then this must have changed after the last release, sorry I didn’t check for that!
Probably best to build SDL_Image yourself from latest git code then.

@slouken @icculus: Might make sense to create a new zlib-license-only SDL_image release?

Here’s the relevant change, it’s just a relicense: png: removed LGPL copyright text, filler comments, and obsolete email… · libsdl-org/SDL_image@c5e4e65 · GitHub