I suspect the reason no images are being returned is because you didn't have GD installed or enabled at the time the images were uploaded. If you are still getting the "no editor" message then that means GD is still not working. But, regardless of whether it's working now or not - if GD wasn't installed when those images were uploaded originally then WordPress was not able to determine the height/width of the image. So it won't have saved that info with the file meta-data and Imsanity will ignore those images.
I would look at your database and find an image or two that are not being found. run this query, fine one of the images and look at the "file_meta" column. You should see height/width information. If not, then that means WordPress didn't save it when the file was uploaded.
wp_posts.ID as ID,
wp_posts.guid as guid,
wp_postmeta.meta_value as file_meta
inner join wp_postmeta on wp_posts.ID = wp_postmeta.post_id and wp_postmeta.meta_key = '_wp_attachment_metadata'
where wp_posts.post_type = 'attachment'
and wp_posts.post_mime_type like 'image%'
and wp_posts.post_mime_type != 'image/bmp'