This mainly just affects the iOS app which uses the API mentioned in the comments.
commons images are always "Last updated 0 seconds ago". except if they're cached somewhere. then swipe down to refresh the page and it should be back to 0 seconds. (or at most 1 second)
See also
The API returns always the current time for lastmodified:
https://en.m.wikipedia.org/w/api.php?action=mobileview&format=json&page=File%3AFEMA+-+25380+-+Photograph+by+Barry+Bahler+taken+on+07-27-2006+in+District+of+Columbia.jpg&prop=text%7Csections%7Cthumb%7Cimage%7Clastmodified%7Cnormalizedtitle%7Cdisplaytitle%7Cprotection%7Ceditable&onlyrequestedsections=1§ions=0§ionprop=toclevel%7Cline%7Canchor&noheadings=true&thumbsize=640&appInstallID=9b6ee9d4-3816-431f-bea3-afb81ecce643
This is not an issue with the app, but with the mobile API returning the wrong thing.
@Jdlrobson: Adding MobileFrontend-beta project as the MobileFrontend-stable project was archived for reasons unknown to me, and its description was not updated where to file tickets instead.
@Aklapper I think we are using the Mobile-Web tag as the main tag for MobileFrontend issues
https://phabricator.wikimedia.org/tag/mobile-web/
https://phabricator.wikimedia.org/project/board/67/
I'm not sure about the Mobile tag though.
AFAICT this is because WikiFilePage doesn't override WikiPage#getTimestamp and the latter will always return now for file pages.