15. A data processing system that is configured to provide input to a workflow application, comprising: a digitizer that is configured to receive a source document having an original signature but no digital signature, and that is configured to generate a digital representation of the source document, wherein the source document comprises a paper document, and wherein the digital representation of the source document includes the original signature represented digitally but no digital signature; a user interface that is configured to receive, from a user, a correspondence of the digital representation to the source document; and a digital signature generator that is configured to sign, in response to receiving the correspondence, the digital representation with a differentiated proxy digital signature, wherein the differentiated proxy digital signature stands for the correspondence of the digital representation to the source document and to a presence of the original signature on the source document, wherein the differentiated proxy digital signature does not stand for an authenticity and an integrity of the source document, wherein the differentiated proxy digital signature is annotated with metadata indicating the quality of the original signature, and wherein the differentiated proxy digital signature indicates the digital representation corresponds to the source document, and further indicates the original signature is actually present on the source document.
17. The data processing system of claim 15 , wherein the digital representations of the source documents comprise image representations.