The Hidden Photos Within Photos 27B Stroke 6

"It's well known that digital photos, like PDF files and Word docs, can contain meta data that leak information the publisher didn't intend to reveal. Less acknowledged is that some cameras also embed a small thumbnail image of the original photo that can survive subsequent tinkering and cropping -- allowing a before-and-after comparison. "

I had no idea that thumbnails were embedded into digital images. I know info such as how the digital camera took the picture and time and date were embedded, but no idea that an actual picture was embedded into an image file. It would be interesting to see Flickr photos that have been cropped or altered and then posted to Flickr.
I'll have to scan my computer and see what turns up.