Imageshack used to be integrated into the 'go advanced' posting option, but for some reason it's no longer supported.
You can still use Imageshack to insert images into your posts (i still do) but you'll have to follow this link. There's no need to sign up for it either.
• Click on the grey browse folder.
• Locate the image you want to insert.
• Click the blue upload now button.
• Click and highlight the 'Forum Code' script.
• Copy and paste this into your 'reply' on GTP.
Q: How about hosting our images online?
A: Many users use ImageShack, Photobucket, or Flickr to host their shots. In addition, below are some helpful explanations on how to post thumbnail shots: