Instead, right click the image, and choose "Copy image URL" or "Copy image location"
Paste the link into your post, highlight the link, and click on the IMG button located above the text field.

*Poof*, instant picture.
Example:
Incorrect
http://www.redwolfairsoft.com/redwolf/a ... _PSG_1.htm
Correct

Bear in mind, this is no substitute to actual pictures of the items you are selling. You stand a better chance of making a sell by uploading pictures you have taken of the item(s).