Display a thumbnail based on post images with no additional uploads. For multiple image posts, thumbnail respects Gallery sort order.
While the plugin will show thumbnails and will not break in WordPress 2.5, the ability to order the Gallery images was not added until 2.6.
Short answer: no. This plugin relies on the way images are attached to a particular post when they are uploaded through WordPress. Images hotlinked from other sites (or even linked to a place on your own server not controlled by WordPress) are not tied to the post as attachments in the WordPress database.
No, but the plugin will only show thumbnails for images uploaded through WordPress. For posts with no WordPress uploaded images, no thumbnail will appear.
This plugin works by first looking for any attachments in the
wp_posts database table that have a
post_parent ID that matches the current post and as a second step for posts with multiple image attachments, returning the attachment with its
menu_order field set to "1". If no image attachments match the current post ID, the plugin returns "false".