Save the accompanying image here and open in Photoshop. Create a duplicate layer. On the dup layer set your brightness to 85, and set your contrast to +65. Note the new image. While you dont need the second layer to achieve this, having it allows you to click it off to view the original image. Now tell me how it's done. I can see that there is a checkerboard pattern in the original image, and that the command is obviously suppressing one pattern in favor of the other, but I really can't figure out the actual dynamics of what's happening because it's just a simple JPEG with no hidden layers. Any technicians out there?

Attached Link: http://en.wikipedia.org/wiki/Steganography

...hmm See why flowers are so popular! I think the pattern is just there to throw you in the wrong direction. [Hint: look at the histogram.] Various techniques. There's a nifty cat hiding at this link.

I have seen this done with a semi transparent GIF, but not when converted to Jpeg, maybe layering a trans GIF over a another image and flattening will work???

That almost appears to be like a transtone filter.But hmmm I am lost as to why.

Simple. The image is masked with another image every other pixel. If you use IE, you can reveal the 2nd image by selecting the image (or just press CTRL+A). The image is a bit corrupt die to jpg compression, it works best with GIF images properly prepared. You see the flowers because they're more colourfull/contrastfull and thus mask the other image.

Thanks all. This forum can answer anything!

Very interesting. that Wikepedia entry is very enlightening. Now, how to do it ourselves...