You can always fetch your high-resolution photos from your galleries. Your visitors can, too, if you choose "Original" for the "Largest size" option in your gallery settings.
Download each one
There are two easy ways:
Method 1: If the Originals are enabled (and you have Right-Click Protection turned off), your visitors can move their mouse over the main image in a gallery. They'll see a yellow folder icon on the flyout photo bar. Click that and the full-resolution original image will automatically download to their computer.
Note: That icon will always appear to you, the logged-in account owner. If you're worried about theft, view your gallery logged out to see what your guests see. (More on image protection.)
Method 2: Alternatively, you can move your mouse over the main image in a gallery and click on Original in the flyout photo bar.
The photo will open in the Lightbox and it could be very large. Simply right-click anywhere on the photo and a small menu will pop up. Choose Save Image As... to grab a copy.