Only your icons need to be that small. Your other pics done have to. If the icons are what you are trying to do, and you have to use a normal paint program (similar to MSPaint which is what I have to use, but you won't have that on a MAC, I have no idea what it is on yours), you basically have to make guesses until you get it right..What I do is try to make it a number that you can easily divide into 200. Like 800x800 cropping, then resizing it by 50% 2 times to get to 200x200. But that will cut off some of the pic. If you want the majority of the pic in the icon, you have to guess with this kinda thing.I get REALLY close to the 200x200 and start going by like 99% and 98% or something like that at a time. It takes forever, but it works.
Other than that..No idea sorry