[PHP] Help : I need modify a the header information in a JPEG image file

[Patricio Vera S.]

    Hi,

    I new to the php world ant the image too, and I need modify the header information 
in a JPEG image file, is that possibly? How?

    I need put some information in the image at the instant when the user download 
this from the web site.

    Thanks in Advance.

Saludos,
Patricio Vera.