Here's the result of posting all the code choices I get from the image hosting site I use (
www.imagehigh.com) for one image I uploaded today. When the image is first posted I get a "Link to Large Image" code that works a treat but is never shown again when you select 'image codes'.
The image part of "Link to Large Image" code:
Hotlink 1 for forums:

- clicking on this takes you to the full size image AFTER a whole load of advertising has loaded.
Hotlink for forums 2:
[img=http://Serv3.imagehigh.com/imgs/04/28388_PICT0969small.th.jpg
- same as above.
Image to friends:
http://Serv3.imagehigh.com/view.php?...path=/imgs/04/
- same as above.
Direct link to images:
http://Serv3.imagehigh.com/imgs/04/2...T0969small.jpg
- opens a new browser window with just the image in it. (Yay!)
My Space HTML code:

- clicking on this takes you to the imagehigh homepage NOT to the pic.
Direct link to images code pasted into an 'Insert Image' box:
[IMG]
http://Serv3.imagehigh.com/imgs/04/2...T0969small.jpg[/IMG]
Direct link to images code pasted into an 'Insert Image' box, 2nd source:
It seems that if you copy the 'direct link to image' code, paste it into the 'insert image' box and then DELETE THE URL TAGS (if present), that will put the full size image into the post.