You can always "hold up an old newspaper". Nothing prevents you from storing and reusing an old signature. It always only proves that it wasn't taken before a

You can always "hold up an old newspaper". Nothing prevents you from storing and reusing an old signature. It always only proves that it wasn't taken before a certain date. You can then also prove "not after" by timestamping the picture (having it signed by a RFC3161 timestamping authority or putting a hash on the blockchain).