Marc, actually the regularity is in image size. You can download big images by viewing them in the full size. As to the small one which does not have "view full size" option and no save as option. There's a small trick - place your cursor on the image and drag it slowly from the center of the image to the edge, you'll notice that cursor will change from a "hand" to the "arrow" When it is changed to the arrow you'll be able to save image.

It happens due to the switch arrows on the left and right sides of the images. They are placed over the images via html and there's a small patch where you can place the curson on the image itself.

This will be fixed in the upcoming update of the photo plugin.

Oh, thank you for your reply. It is not so much that we from the admin team want to download photos but our members. And for them the simpler the better :)

Then we wait for the next photo plugin update.