I'm not familiar with ImageShack but it looks more like a place to store your own images for posting elsewhere, than a place to borrow images from someone else.

As a Psych Central member, you can upload images to one or more albums located on your profile page. You don't seem to have created any yet. Find the My Profile link at the upper left of this page or any Forums page:

Clicking on it takes you to Your Control Panel (left column). The 7th link down says "Pictures & Albums".

Once you have an album set up, you can upload images to it from your computer (assuming you already have some stored there) and link to them in posts, PMs or VMs. It saves you the trouble and possible expense of setting up an account at an image-sharing site. Even when those sites are free, they often keep reminding you how much more you could do if you had a paid account.