Photo size not square? KBs or Res?

New to this forum. The photo uploader says 800x800 photos and yet I have seen rectangle photos 4x3, not square? Is the 800x800 the maximum resolution, or is the uploader more restricted on the KB size? If so, then you could upload a higher res photo? I will try this.

Maximum 800 in both dimension, but can be lower. So 800 x 600 is fine for example. Maximum file size is 250 kB. You can upload larger images, but they will be compressed below this and can look a bit bad, so it's good to get the file size below this first yourself and check you are happy with the quality.