This screen shot demonstrates how/where to enter the image dimensions in
Photoshop. Be sure to use the correct unit - in this case px (not inches).
Photoshop allows you to dial in the exactly right image dimensions at the start
of the process in one easy step. You end up with the exactly right aspect
ratio and the correct image size and the correct file size.
The entry shown is correct for Denver MLS. If you are not in Denver,
it's important to consult your local MLS and make sure you crop and submit
according to the specifications of your MLS.