
Karim S. answered 08/26/19
Fun and Patient Art Teacher
I can't recommend the best app for this, but many people use figure posing apps, i.e. EasyPose, to put human figures in the position they want. You can then trace the image.
Personally I do collages in photoshop with images I find on Google Images and then trace the collage. Photoshop lets you adjust size, color, foreground / background, etcetera