Automatically adding code into img tag

Ok so my topic subject line doesnt make much sense, so i’ll try and be descriptive here.

Basically all I want to do is have WordPress add ‘rel=”lightbox”‘ into the image display code so the code goes from looking like:

‘< a title=”IMG.jpg” href=”URL.jpg”>’

to:

‘< a rel=”lightbox” href=”URL.jpg”>’

And yes, I want to replace the ‘title’ tag with the rel= tag.

Obviously I could edit this in each post I make but that would ultimately be more time consuming. It would be far easier if I modified the code of WordPress so when the image uploader sends the code to the editor it already includes the rel= tag.

Hope to get some help on this soon.

Nate Lanxon