Here I shall introduce the art of えあう / Eau, an artist who has produced a number of these interesting illustrations, which as you can see use photos as a base. Whilst doing this and not disclosing it seems to be a recipe at times for derision or even scandal, doing it quite deliberately seems to be well received, and looking at these images, who could disagree.
Below you can see more of his art, and some of the source photos.
Unfortunately, identifying and assembling all the photos used as a basis for this art is not really feasible, but I can easily provide a few.
This apparently is a photoshop of seiyuu Aya Hirano (Haruhi), now being re-renderd into Haruhi herself:
I know I’ve seen these two somewhere…
Another modest artist, Eau claims not to be able to draw properly, so he mostly concentrates on learning though these transformations.