Hi Guys,
Is the small picture that you are talking about the one I've circled in the attached picture? If so, these are called avatars and the size of these pictures are reduced to a smaller size automatically by the application. They are only intended to represent the member and quickly identify them and because they are reduced down, the quality of the picture is lost and only the original picture would be suitable for enlarged viewing.
When it comes to web based applications, it's the size and number of images on a page that impacts how fast a page loads so things like avatars are kept and displayed as small files and attachments are first displayed as "thumbnails" first and can be expanded into the larger pictures by clicking on them.
Thanks,
Chris