There is a size limit, to enable most people to see on different sized monitors, and to ensure that pictures load easily I guess (though that is more Smoo technical stuff!)
I usually do my pics as a maximum 800 x 600 pixels, which always seems to work.
Leon is adorable, and I would agree a lovely cream satin banded. On a shorthaired hamster the satin really darkens the colour so much, and gives it a really plush look, just as you have caught in your pics. Well done on that, cause taking photos of satins can be really hard!