how to add the thread title to the images alt atribute????

[kootta]

in vbulletin the users posted images they have an empty alt attribute
like that

<img src="
" alt="" border="0"><br>

the alt attribute is empty i want to add the thread title in that attribute
so the code look like

 <img src="
" alt="how to add the thread title to the images alt atribute????" border="0"><br>

i hope someone can help or someone guide me to a product doing the same?
thanks