Envira Gallery Protection Addon GPL Overview:
The Protection addon disables image right-clicking in both the gallery display and lightbox views to prevent visitors from downloading your images.
Using this addon is easy – all you have to do is activate it! After activation, the protection addon will be automatically enabled for all of your newly created galleries. Existing galleries should be updated to have image protection applied. You can turn off image protection on an individual gallery basis by unchecking the “Enable Image Protection” option under the Misc tab in the gallery management box.