My girlfriend has set me a tantalising puzzle: she is able unerringly to 
discern a difference between certain images which I cannot do, and I don't 
know how the hell she's doing it.

It all started when she set me a link to an online game 
http://members.iinet.net.au/~pontipak/redsquare.html. You need to move the 
red square so as to avoid the blue squares which move around, and also avoid 
the walls. When you eventually fail, it displays a message telling you how 
long you've survived. We've been sending each other screenshots as proof of 
how far we've got and she pointed out that if I got desperate I could try 
faking the image screenshot by editing the image and putting on different 
text so it looks as if I've lasted for longer.

Now to the really intriguing part. I produced some fakes by taking the 
existing image and modifying the text (erase old text, put new text (same 
font) in its place in exactly the same position) and she was able to tell 
very quickly which were fakes and which weren't. I cannot see any difference 
between the real ones and the fakes, apart from the obvious difference of 
the exact digits. Subtracting the images (real-fake) in Paint Shop Pro shows 
that they are otherwise identical.

I've established that:

- the digits in the times are irrelevant - it's not that program cannot 
produce certain times

- the fact that I've included a bit of background image of parts of the game 
window is not relevant - I could have cropped the images to show only the 
dialogue box and she'd still have been able to tell.

- she's simply viewing the pictures in MS Fax Viewer or MS Photo Editor: 
she's not doing anything very tricky like examining the bytes in the files 
for some "number of times edited" attribute

- she could see the difference at actual size though it was easier to see 
when the images were zoomed; she also needed to compare my images against 
the real output of the program

The images are:

http://img233.imageshack.us/img233/3223/11302fj7.png

http://img87.imageshack.us/img87/6038/11458eo4.png

http://img81.imageshack.us/img81/8566/12657bx7.png

http://img87.imageshack.us/img87/4152/16687vi4.png

http://img134.imageshack.us/img134/6697/14364vq9.jpg

http://img206.imageshack.us/img206/48/16641sh1.jpg

For these last two, she said that the real image and the game have some sort 
of imperfections in the text of the "You survived" message whereas the text 
for the fake is "too perfect". Buggered if I can see any imperfection in the 
text of one picture!

She believes that it's a difference which any reasonably observant person 
should spot, but it's got me and various other people baffled.

I'm at the stage where I think that somehow what she's seeing on her PC is 
different from what anyone else is seeing!

Any help will be gratefully received: I want to be able to go back to her 
and say "this is how you are doing it". There is male pride at stake ;-)