If you remove, let’s say your cousin Bob, as a contributor to your picture or album, he will no longer have the access. To him, it's as if the picture or album is no longer there. You would remove him by clicking the red "x" to the right of his name in the list of contributors.
If he still has the invitation email, and clicks on “View on Ponga” after his invitation is revoked, he will get an error message saying the link is not valid. He will no longer have access to the picture. Similarly, the picture will no longer appear in his All Pictures view where shared pictures appear with a little arrow in the bottom right-hand corner of the image tile.
The same is true with shared albums, except of course all pictures in your album will no longer appear in Bob's All Pictures view, and the album will no longer appear in Bob's list of albums.
If Bob looks in the “Shared with Me” list of pictures, the picture or pictures will also not appear.