There are cases where members (including yours truly!) would like to allow visitors to download images. Typically, we have a couple layers of protection to specifically prevent that - to protect your photographs.
We've added a checkbox in the Album dialog to turn on a button when viewing images, that lets visitors download the original image file.
This has been added to the default template and a few optional templates - we'll have the rest of the templates added shortly.
To enable image downloads (which are OFF by default), go to the album, click Mange Album at the top, and check the "Enable Downloads" checkbox, then hit save.