I am trying to write out a message indicating whether an image has been changed or not. Its a signatures database, and I want to place an audit trail on it, so that I can tell if an image (signature) has been tampered with.

On open of the form I have set 2 variables:
Public Sig As Image
Public NewSig As Image

On current I will set Sig and NewSig to be the image in the field signature..
Then after update I will compare the Image set as Sig with what is then current in the field which I'll set as newsig.

I'm having a problem where the Signature field is empty ie:

If IsNull(Me.Signature) Then....

I probably need to do this another way, as I get a type mismatch error. Any ideas?