Posted: 28/10/2015 at 18:54
It's definitely file size - anything under 1MB will work, no matter what dimensions it has. If your photo editing program allows you to change the jpeg compression, do that rather than resize. As a rough guide, I have no problems posting 3000x2000 pixel photos with a jpeg compression factor of 70 (where 100 is least compressed.) Some editors use a factor of 1 (least compressed) to 12 (most compressed) just to confuse things, so you'll need to experiment to find what factor works on your photos and keeps file size under 1MB.
Hopefully, the new site will take care of all of this sort of thing for us.