Can't Recolor Particular Wall Painting

I wish to recolor the landscape shaped painting Dogs Night In, but for some reason it is becoming distorted after I choose it initially on the objects page. On the page that has the tabs Catalog, Texture, Meshes, and Tags, the picture of the painting on the left (the one in the grid) is perfect. However, the picture on the right is crushed into a square shape. This causes the dog picture part of the picture (as opposed to the frame) to become portrait shaped and stretched. When I export this to my desktop, it retains these incorrect proportions and I can't use it in gimp to recolor it with my picture that is a landscape shaped picture.

Any help you can give me so I can fix this problem would be greatly appreciated. Thank you in advance.