Many of you will know this already, some may not but here's the inside scoop on TT pics:

Avatars:
The pic next to your comments is an Avatar. It's changed by going to the "Settings" tab in the top right of the web browser.
Once the setting page loads, go down to "Edit Avatar" on the middle left of the page. Then, follow instructions for linking to a web based image or uploading one directly.

Pictures in threads:
This forum can store images but they're seen as thumbnails when you upload images to threads.
If you want the image to appear full size, first upload it to somewhere like flickr, imgur, photobucket etc..
You can then link to the image via the "insert Image" icon on the comments, with "Retrieve remote file and reference locally" unchecked to retain the image size you want.

Hope this helps!!