Does dpreview gallery recompress photos?
I did the test you suggested and recompression is evident, they leave unchanged the pixel size though.
Pity, because the slideshow is nice, but recompression is so strong I could notice it even with no zoom, then zooming, and even more comparing original vs full size dowload, revealed the problem.
|Morning At Picture Lake by Buzz Lightyear|
from Dawns first rays
|AT-6 Harvard by jarud|
from Trainer aircraft
|Matterhorn by ewng|