Quote - Google image search, look for astronauts footprints, then make your own brushes out of the best you can find. The larger the image you can get, the better. Best advice I can think of. That's what I did when I needed to make some footprints in snow for a project. I didn't make a brush, I made a displacement map, but same principle.

That's the best advice I could give too rgarding creating the brush. As per chaging the direction of each footstep, here is the solution if you own a wacom intuos: get yourself a wacom 6D art marker pen. The marker pen will allow to rotate the direction of the brush just by rotating it in your hand. I hope this helps.

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