It won't let me get my own skin- I choose it from photo library but it comes up invisible

I want to change my skin to a cute turtle but when I go into my photo library and choose it (it is a minecraft skin by the way) it asks me to choose female or male so I just choose any because it's the same on both but then the skin comes up as invisible and I can't play the game because it says "error with skin" so I have to change it to Steve or Alex