Theres a couple of ways… some kind of filter
One option is to prefix or suffix the thumbnail image with something so the full name is project-thumb.jpg, then setup a custom filter letting you filter on it described here
Another, messier way is to use to use a field in a files meta data to set a field and then filter on that.
As a side note, this is better way to do your alt tags, rather then using the page title. Using file fields will let you set a alt tag value for each image.