Cleaning the clipboard doesn't solve the problem...even coupled with turning off the entire keyboard it will only keep those who are making a half-hearted attempt to copy the signatures out. For instance, I would just start a screen capture program that actively recorded the desktop and then bring up the screen containing the sensitive information. A Voila, I have an AVI or MPEG file with frame after frame in it of your signatures. Then I can cut-n-paste them at my leisure.
What needs to be concentrated on is some type of security device to keep the user from seeing anything except the signature(s) that him/her have rights to access. I would go with some sort of security login and tie certain signatures to that login, so when they go to pic one it will only bring up those they made.
Another idea, distort the images to the point where though they are still readible they could never be mistaken for the original signature image if they were copied. this could include multiple areas of distortion on each image so they would be next to impossible to undistort and also maybe a word like "VOID" or "SAMPLE" written across them so though they can still see them. This may be overkill, depends on how sensitive this data is. It may be enough to just bring up a low grade thumbnail of the signatures so that were they to be copied and then resized back to normal they would lose enough to make obvious for the copies they are.
If I think of anything else I'll let you know...I feel like I am out of ideas for now.
Slighthaze = NULL