Setting screenshot format?
I don’t think you will be able to set it to png, but the jps thing may be set on the keybinds.
Also, are you running with 3d enabled?
The setting in question …
There is also a way to set it to .bmp instead of .jpg.
http://wiki.guildwars2.com/wiki/Command_line_arguments#-bmp
I found the problem: I must have bound End as Stereoscopic Screenshot at some point, my laptop has End and Print Screen on the same keys, and the FN was defaulted on.