I understand that, but i guess the mod wasn't talking in MB, because no image grabbed from screen (well never say never lool) will have that size in Kb/Mb.. (normally my photos in the past had between 150kb and 400kb)
The automatic reduction of the images that forum does it's on the pixels to fit on their standards (that's why almost all the photos have the same visible size but if you click on them they could have totally different resolutions/pixels