First, get rid of the text, if it's in the image. Then threshold the image to binarize it. Then label the image with bwlabel(). Then use ismember to get rid of blob #1 and keep all other blobs. This assumes that there is no strand of brightness that connects the skull to anything inside that you want to keep. So, it's like 2 or 3 lines of code. See if you can do it yourself first, but let us know if you can't.