Could be die chip(s). If you understand how a die chip is created, then you can sort of put the pieces together in your mind to see how this could happen. I'm not sure they are chips, but seem likely as it is not a crappy Zincoln with bubbles.
Pictures are a little blurry (see the attached files for some photo ideas) but looks like die deterioration. A good indicator is the direction of the material flow (towards the rim. When the dies are approaching their limits (LDS, VLDS), the ghosting around the devices gets worse.