I see the 2nd shot having a layer of artifacts put on it on almost every edge visible. Also geralt's back/clothes appear desaturated, loosing some of its color. All in all it might not be that easy to spot but considering the image itself is very "noisy" to begin with that's not surprising. If one takes a clean game with tons of edges, like for example Mirrors Edge and then rape it with compression - then it'll be much easier to spot.
I took an old Mirrors Edge screen of mine and uploaded it both to imgur and abload, then cropped them and reuploaded them both to the same site. In this scene it is painfully apparent what compression does to your screen, it is almost akin to bumping down the visual settings a notch in conjunction with having slapped on a blur filter, the loss of detail is obvious :
http://h11.abload.de/img/abloadj6j9e.png[IMG]
[IMG]http://h11.abload.de/img/imgur0tj2t.png[IMG][/QUOTE]
But how did You uplod that screenshot to imgur? Have You compared that PNG to 100% JPG? Because even 100% quality JPG desature shots a little, its most noticeable on red colors and some on green.
You have to upload 600kb files to imgur to avoid additional compression [it should be 1mb as their site says, but its not unfortunately ;\].
Can You post link to that shot in png/bmp?
Ps. I have never said that there is no difference between PNG and JPG [it has to be], but its almost not noticeable even when You compare both shots directly.