A link to your site will always make it easier to see what’s going on!
From your description, it sounds like your theme includes a javascript file that the theme includes gives a lightbox effect to all images.
I looked up “expose” and it looks like you have the Expose Gallery theme for ThemeForest from kriesi.at?
That theme includes prettyPhoto, another lightbox. That is probably the issue, but I would have to look at your site to be sure.
According to kriesi.at, this is what you need to do:
Add this class to disable it on single images:
class="noLightbox"
or, to disable it completely, open up the js/avia.js file
and comment out this bit:
It will look like this
//activates the prettyphoto lightbox
if(jQuery.fn.avia_activate_lightbox)
jQuery('body').avia_activate_lightbox();
Change it to this
//activates the prettyphoto lightbox
//if(jQuery.fn.avia_activate_lightbox)
//jQuery('body').avia_activate_lightbox();
I don’t know how familiar you are with digging through the code. Let me know if you need help.