Signing PDFs digitally became more common in the past two years. Unfortunately, most people got used to proprietary tools that they already know and now instead of not accepting digitally signed files (and actually checking the integrity of the certificate used for signing), a lot of users only check the visible hint. In most cases people expect that the visible hint should look similar to one generated by one of Adobe's product (including picture of signature).

In recent versions of Okular, you can digitally sign a file by drawing a rectangle where you want to have the visible hint for the electronic signature. However, it only includes text with the name of the signer and date. This should be fine for most cases, and I don't want to start a debate on how wrong is to include a picture of one's signature in documents, but it would be nice to have an option to include a picture of signature into the visible hint.