Hm that is weird. Let’s hope that someone with more Apache knowledge comes along and knows how to debug this.
Ah yeah! diaspora* transforms the files a bit, including stripping private metadata (unless you have disabled that in your settings), and it also rescales the file into different versions for thumbnails etc. However, both of those files are fine - none of them is a APNG. In fact, you couldn’t even upload a apng if you tried.
And it’s even weirder, because diaspora* just stores those new versions to the disk, it does not actually serve those files. We leave the static file serving up to the reverse proxy (in your case Apache), because those things are really fast at delivering statics. So something is making your Apache send a apng content type for
.png files. That issue is not just affecting uploaded files, though - even your Favicon (https://social.schwend.us/assets/favicon-158d223c914fb4936d3b14294dbc3f0d4d87ffced0694cc013cca43910ef2324.png) is served with a apng mime type.
Just for reference, can you share your entire Apache config with us? Just paste them here as a response into code blocks.