Insert image through button

Hello there,

Is it possible to insert an image through a button?

And a step further, to protect the function of this button by a password.

If not, maybe there is another way to do the following:

One user must verify the form and use his initials (which I have as .jpg).

But not everyone must have the change to use his initials by clicking the button.

I'm using Adobe Acrobat Professional 9.0.

I have already did some research on the net but withouth success!

Thank you for your replies.