Message: Something went wrong, could not validate the uploaded image.

What are reasons for this message to appear in the 'upload photo' box before a photo has fully uploaded (i.e. before it could fail due to the many reasons given in

The photo is of an old military plane that doesn't have any other images in the database, is 1280 pixels wide, jpg and meets the minimum stated size of 250kB. In case it was the crop I tried 3:2 (out of camera), 4:3 and 16:9. All variants gave the same message.