Those should be photos associated with your Google Picasa account.  That would include images from Blogger as well.  I've been trying to find a way to remove them as well with zero luck. 

I just grabbed another gallery app that allows for more customization and have been using that instead of the default one because of this. The images seem to sync up as soon as you connect your Google account to the tablet. 

I've reflashed mine a few times with different firmwares and keep ending up with the same thing.  This will likely be returned and exchanged because of this.  The main reason I bought this tablet is to use as a digital portfolio for stills and videos of mine.  So stuff like this is a pretty big deal.