Its many different ones. I mostly do my collages on my phone. The artwork I use for my collages is from those old 50s EC comics. First I cut the scans of the comics with an app called "Background eraser". After that I combine the collages with another app called "Face changer 2". Then I go to the App Pixlr, heighten the sharpnes to the max and put a black and white effect over it. Afterward I go to a site called Photomosh and there I Posterize my artwork and put differetnt effects and colours on it to see which ones best suited for the collage. Lastly I upscale the finished work. It would probably be easier to do all that in photoshop, but I kinda like how time consuming it is.

Sometimes I also draw on my collages to add extra detail. Here I had to draw a longer robe for the skeleton and also had to add those stars in it.