One of my members just asked me a question about a number of avatars that weren't loading. Upon looking into it a little more, it turned out that all the ones she could see were not PNGs, and all the ones that weren't loading were PNGs. She also said she's had this issue on other SMF sites (within the last year, so 2.0+; I'm running 2.0.7 right now), across all browsers. She's running OSX 10.9.4.
I'm not having any issues with PNGs loading, and I haven't heard that anyone else is. Searching around hasn't gotten me anywhere yet.
Anyone have any clues or ideas whatsoever? Or is this a weird fluke and completely unrelated?
If she is having the problem and you are not, then I believe the issue would be on her computer...
To try to isolate the problem, can she try a different browser?