Add Written Signature to PDF

I want to add a written signature to an existing PDF document. 

I would prefer to use an Image XObject in an annotation, but unless I'm overlooking it, there doesn't appear to be a way to create an annotation that shows an image.  So now I'm thinking that the only way to add an image to the page is to create a content stream that shows an Image XObject, and add the stream to the page's '/Contents' array?

The other way that I've found is to vectorize the signature and use an Ink Annotation, which seems pretty straightforward, but would require a lot of changes to my signature capturing system.

Any other options that I'm overlooking?