I've seen several photos like the example below and I would like to create one. I think it overlaps a profile photo and a front headshot, with lots of local adjustments. Do you know of any (photoshop) tutorial explaining how to create it?
It's a very clever and effective trick, but provided you have good quality source images it is not that difficult to achieve.
You need to overlay the profile and frontal images so they match up at the corner of the right eye and corner of the mouth (shown by the green circles). Then it's a case of blending between two layers along the red line.
Certain parts of the image might have to be nudged using the liquify tool (or similar) to line up better and there is evidence of this in the example you posted.