<img src="URL">
Just put the URL of the image in the quotes
Or you can get fancy like this:
<img src="URL" alt="Image Not Found" align="center">
This way, the image will display a "Image Not Found" message if the image is removed and will be centered.
Also, if the image is huge, I recommend limiting the size, like this:
<img src="URL" alt="Image Not Found" align="center" width="400">
If you want to use one of your own MySpace photos in a comment, right click the photo and select "Copy Image URL" or something similar to that (depending on the browser) and use that as the URL