Yeah, that pic to the left is your Avatar. You can get there by going to 'Your Control Panel,' then select 'Personal Info.' Once there, go to 'Avatar Options,' and you should be able to choose an image already in the gallery or upload your own image. Hopefully that should help.
Here a link to the posting pictures thread. Not the Avatar, but pictures in general. If your reduce you're image size prior to uploading them to the server, then the window will stay the normal width. I think the max width is about 500 pixels.