Also, in Pawtucket, you have 2 ways to display Collections:
- "Browsing" menu > Collections
- "Collections" menu
In order to display linked image in the "Collections" menu, check the file /themes/<your_theme>/conf/collections.conf
It should have somewhere:
description_template = <table><tr><td>^ca_object_representations.media.icon</td><td>^ca_collections.description<br />(^ca_objects._count objets)</td></tr></table>
or equivalent. You can change the size of image by changing "icon" by another preset size (such as "thumbnail", "preview170", "mediumlarge", "medium", "widepreview", "widethumbnail", "tiny", "small", "preview")
But probably it's just "accessible to public" missing for your images, as said @jeffschneider.