Ha! I just figured it out. My fields were not blank but contained a single space for fields that were blank. Seem the code I used was right I just had to change it to:
<?php query_posts('&meta_key=imgs&meta_compare=!=&meta_value= &orderby=rand&showposts=10'); if (have_posts()) : while (have_posts()) : the_post(); ?>
for it to work. Hooray!
