i'm sure you can use programs like gimp for that, but i used some website?? i don't remember it atm but i can link it when i get home, heh. using thst website is very easy, at least for what i've been doing (which is mostly making things bounce, if i wanted to do something that actually changed the picture i'd probably use something else)
it might show up if you google "animate pixel" but idk i will link it 2 u later okiedokie