Regarding image sizes, it is, of course, the responsibility of the individual forum moderator to order in my experience on other sites unless there is a general ruling (which I do not see on PPrune).
Heliport - you need to understand that '1024' includes the side bars on a forum display, and even viewing your forum on a 1440 screen, images at 1024 are 'off the side'. 850 is a far better size. On PPR I guess the available width would be about 8-900?