Copyright Lawyer Needed US / worldwide

Hello,
I Talked with some people and this should be a life changing job both for me and for the lawyer!

I need an attorney for some cases of copyright violations that I found on Facebook and it’s about the photography whose creator is my father,
he is a renewed news photographer in Serbia and somebody took one of his rewarded works and created meme out of it, now there over 100,000s of reposts and shares and more than 5 million likes across the Facebook and other websites as well, on , Instagram, linkeding, Twitter etc.
so there is really many people who separately posted this photo without any rights so it’s violating the copyright of my father and I would like to see if there is something that we can do about it, what should be my next steps if I want to see sue those people and what could I expect from it?

I would like to work on percentage as the final amount will be really huge

I have much more details,
message me and we can set up a video call and discuss all details,
Thanks