A new PBase member who is starting to scan and post pictures wrote me to ask how to prevent other from printing her work. Here is my reply:
I like to post pictures that are 800x533. This allows people with high resolution monitors to enjoy the detail of the photograph. I compress the picture to 60% quality for jpg to save space and speed up downloads. It doesn't seem to affect the image quality too much.
A Kodak brochure on digital photography suggests the following minimum standards for prints:
1 Megapixel (1200x800) = 5x7 print; 2MP = 8x10; 3 MP = 11x14.
I find this too strict and have produced excellent prints from much lower resolution images. A bigger factor for prints is the quality of the printer and the paper. Costco or Sam's Club will produce beautiful inexpensive prints from low resolution images. Someone could go to my PBase gallery, download an image and print an 8x12 that would look great (image quality wise). If they want to just download the image to view their PC, it is even worse since printing requires more pixels and better image quality.
So how do you protect your pictures? You can lower the size you post to 500x333, lower the image quality (highly compress the image), put a giant watermark across the whole picture (please don't), or discretely put your name in the corner. Except for the last suggestion, the other suggestions will reduce the viewing enjoyment of others.
The final thought is philosophical. Why do you want to prevent others from printing your photos? Unless you mark your gallery as private you are hoping that others will come and enjoy your photos and maybe leave a kind comment . If someone downloads your picture and prints it out it means you have given that person something he/she especially enjoys. It is true that you are not justly rewarded and maybe it is stealing, but I am assuming you are not using PBase to sell your works and you are not a professional photographer. The person who downloads your picture and prints it without permission would probably never pay you for it if it was offered for sale. There might be a rare case where someone downloads PBase pictures and sells them as their own work at an art show or swap meet, but that person is probably downloading Francis Toussaint's or some other great PBase photographer's work.
I have had a surprising large number (6+) of request from people for permission to use my photographs. Some have been for web sites. Others have been for educational purposes. If someone is kind and honest enough to ask permission I have always granted it for a nominal fee or for free if it is educational. I do ask for proper photo credit. I don't use PBase to make money, so I'm not afraid of others ripping me off. I use PBase because I like to show off my work, I love it when someone leaves a positive remark on my galleries and because I enjoy looking at other people's work.