Yeah, using template conditionals, you could have an image show in the postbit if a user has one to the creator of that post only.
The syntax is pretty simple for template conditionals, try reading up on it at vbulletin.com/docs/
To get your started, here is what I use to display a side bar tag in my users postbit via a custom field that members can edit.
Code:
<if condition="$post[field15]">
<div><img src="$post[field15]"></div>
</if>
That will display an image if that profile field is not empty. You will need to add on to it but its a start for now.