I recently tested Samsung Galaxy Tab 10.1, and also my kids got a chance to try it out.
Of course they immediately took some silly photos and some how managed to put them into the "Picture Frame" widget which was shown on the home screen, immediately after opening the device.
As the device is not actually mine to keep, I needed to remove the photos my kids took. I used gallery to search the images and deleted the chosen image files. To my surprise, the removed photos were still displayed on the widget!
I tried many different things, I removed all the gallery related caches and image indexes, but the photos were still persistent in the widget.
Finally I removed the whole widget from the desktop by keeping the widget selected for a few seconds, and then dragging the widget on top of the trashcan icon in the upper right corner. After removing the widget, I added it back again and added some photos from the gallery to it. And no more silly photos were shown!
This was the only procedure I could find to remove unwanted and already deleted images from "Picture Frame" widget on Samsung Galaxy Tab 10.1. I guess the widget makes some kind of own cache to the disk, but I was not able to find another way to remove/clear the cache than removing the widget and adding it back again.