This may just be a result of how the PDF was saved. I always find PDF files given to me have images sliced, words separated, strangely placed clipping masks etc. and generally there isn't much that can be done about it.
If it is just a bitmap image then you should just be able to open it in Photoshop and save it to another format. If it is a vector image though, you may have to manually fix it by deleting any clipping masks and using pathfinder to join all the shaped together again.
This is all based on the assumption that the image has actually been split, it may just be something overlaying the image as Kaylee said. Without seeing the actual file it's hard to tell.