Protected Photo Files

Is there a way I can "lock down" photo files I send out by e-mail so that they cannot be altered by the recipient? I know I can click on properties and mark the file "read only", but will that prevent them from also clicking on properties and undoing my designation? How can I send photos by e-mail in a "look but don't touch" format?
Please advise.

Paul - I've never heard of such a locked format, unfortunately. Maybe someone else knows about something like that.

PDF is as good as you can do it with. Any reason?