getting closer I tried the exact url plus and now at least I get an error
<img src="http://domain.ca/phpThumb/phpThumb.php?src=/hart/images/uploads/{exp:extract_url_plus show="& filename. % extension"}{main-pic}{/exp:extract_url_plus}&w=50" />
brings up the phpthumb error
“/home/user/public_html/hart/images/uploads/ No URL Found” does not exist
if I try to use just {main-pic} in my template I get this output when I view my page:
