hey comfy,
when i click on my .jpeg file, on my computer, it opens with Windows Photo Gallery. it may be different on your computer but if, by using windows explorer, you click on your picture and it does open in windows photo gallery then if you click on <file>, then <properties>, you will get all the information about your picture. of course your picture may be in a different format, like .tiff or .bmp but if it is a .jpeg then here are my properties: file size is 113KB, dimensions are: 640 X 480.
start by creating a picture with these dimensions and see if that works for you.
good luck, champ