If you post is showing image thumbnail in the post instead of the full size, then you could change this if you wanted to.
Thumbnail sometimes can be hard to see and cause your reader to click on it before they could see the full image.
1. Log into vBulletin admin panel.
2. Select Options under Settings on the left hand side.
3. Choose Message Attachment Options from the option list.
4. In View Attached Images Inline section, select Yes, full size from the drop down box.