The ImageShack Toolbar will make your life alot easier when posting screenshots! It's implemented into the bottom right of the post-reply interface.

After selecting a file and clicking on "host it!", a new tab will open. The page will be white while uploading, just be patient - duration always depends on the size of the image. After the upload is done, you'll see a page like this:

Copy the direct-link (red-marked) and wrap the URL into BBCode like this:
- Code: Select all
[img]http://img238.imageshack.us/img238/3541/isbox.jpg[/img]
Done!
Images that are bigger than the post-area will
automatically be resized and converted into a lightbox-object. On click, it will open the image in full size, you don't have to worry about any of that though - it's all being taken care of by the magic in the background!
