Error creating PDF signature background with Images2PDF

Converting a JPEG file with Images2PDF gives a PDF which cannot be used as signature background in Acrobat Reader.
If you save a flat PDF in the local user folder

you can use it as a background for digital signature appearances. Creating the PDF with PDFCreator works fine; creating the file with Images2PDF gives a blank, opaque bakcground and/or an error when creating the signature appearance.

PDFCreator v 2.1.1