If you are trying to extract the distinguished name from a certificate-based digital signature together with the accurate digital signature time stamp, that is doable but it is not a trivial task.
Seems like what you're referring to as an image stamp is the image portion that is uploaded onto the PDF document at signing time, and such image file is used as one of the signing options which compliments the signature creation appearance.
That image file is saved locally in the computer where that document is signed.
There is no real easy way to extract that portion of the digital signature field once it was signed.
I've been trying to do that myself for over a year with no success.
The way that certificate-based digital signatures work is very complex.
Digital signature field objects hold various types of layers to organize how data will be extracted from a digital certificate and how it will be positioned and resized, encrypted, compressed, secured and displayed in such signature fields ; that includes where the customized logos will be positioned and maintained in relation to the other signsture field layers ( like the Adobe Acrobat logo, for example).
You may, however, be able to extract some information as I mentioned earlier, and use that information to customize a stamp.
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