In the next week or so we'll be updating Fotaflo so that it's easier to select and deselect multiple photos at the same time. This will also work anywhere else that you can select multiple items for performing bulk actions.
Here's an example in the catalog. First select the starting photo in the group you want to select. Then hold down the shift key and click the last photo in the group. You'll end up with all photos, including the first and last, selected.
You can also select the last photo first, and you can even use this to deselect groups of photos.
This should make it easier to select a large group of photos that are in order in the catalog for faster delivery.