Azhdar: I found this
, and I'm interested to find original source and photographer of each individual portrait. For example, I copied [url=http://i.imgur.com/QdO70Ij.png]this one from original image, saved it as a new file, and then uploaded it to Google image search. But Google can't find it. I guess the source is Flickr, but how to find that specific image? Because I think Flicker does not have reverse image search feature.
It looks like the majority (if not all) are from Vít Hassan's flickr page. The collage you have is made up of mirror images of each photo which helped to obfuscate the reverse image search results.
Vít Hassan's flickr page:
https://www.flickr.com/photos/vithassan/albums/with/72057594101975762 Concentrate on the albums from Sudan such as "Portraits in Sudan", "Southern Sudan", "Northern Sudan", etc. Remember, you are looking for mirror images.
Possibly the person who made the collage from Hassan's photography:
http://adilsud.blogspot.ca/ EDIT: take a look at the description he/she writes on the right-hand side along with the collage here:
http://adilsud.blogspot.ca/2011/07/famine-in-africa-point-of-view.html Here's another idea: take the images you cut from the collage and mirror image them, and then do a reverse image search. Might be able to get a quick match that way.