i'm not sure what p ex is, but this place isn't a stock warehouse of free images to use take and sell. if you want to sell here you must take your own image and make your own images. even if someone allowed the painting of an image, why would they want to be competed with their own work? and if you do buy stock, be sure to read the rules about what your getting. because sometimes you may not be able to resell it in any form.
using a subject - like a person? no. everything should be your own.
---Mike Savad
MikeSavad.com