One of my favorites techniques to use in abstract photography is multiple exposures. Many cameras have the ability to take multiple exposures including using phone apps.
While I haven’t done much with phone apps, my Fuji cameras are capable of double exposures. And my Ricohs can make 5 exposures in one.
In a way, making multiple exposure photos is like making a collage. However, with my cameras you need to take each of the photos within a short amount of time. I like the element of chance that this limitation imposes as with the photo above.
I understand that with many DSLRs you can also take multiple photos in one and that you can do that well after the fact.
I have also made a number of multiple exposures taking photos of my photos from computer and also using books and other kinds of images. The above photo is an example.
I strongly believe that there are very few limitations when it comes to creating abstract and abstract street photography. And it’s always fun.