How do I put an image on the guestbook. Or how can my visitor post images...please help.

Assuming that you mean Bravenet Guestbooks.

Upload the images to your Bravenet photo center and then get the name of the image from there and place it in a regular tag to link it into any Bravenet guestbook.

Your visitors will need to put the images in their photo center or on their paid web hosting to use them in your guestbook.

I will try it. Thank you..