The answer to this problem is the "MANUSCRIPT ILLUMINATION". Hence, the realism, symbolism and complicated imagery found in Northern Renaissance paintings originated in and was influenced by manuscript illumination. This is embedded and implemented with miniature illustrations, with initials, and with borders. There are also decorations and illustrations of books and letters with pictures and nice designs.
The Artist just filled in the blank part around the hand-print. I pretty sure that is what the artist did. If I didn't help I am sorry. I hope someone else can help you if I couldn't