Photo requirements
The rules portals actually enforce, copied from their notices, with a preset that applies all of them at once: pixels, format, maximum and minimum size.
How these rules are kept
Every entry names its source, links to the publisher's own page or notice, and shows the day it was last checked. Issuing bodies publish these rules inside PDF notices that change each cycle, and a preset is removed when a portal stops taking the file, as SSC did for photographs. Confirm against the current notice before you upload, and tell us when one has changed.
A portal that is not listed
Read the pixel size, format and size limits off the notice and enter them in the fit-to-size tool: the options panel takes an exact width and height and a minimum as well as a maximum. That is all a preset does.