Is the skeleton meditation of Buddhist origin?
Yes it's a Buddhist teaching. Contemplation on a skeleton is called atthika-sanna in Pali. Buddha's teaching of this is in Atthikamahapphala sutta (SN 46.57), however, there's no English translation of this .This technique is commonly used by forest monks to overcome sensual desires. You can practice it with a real skeleton, a picture of it or visualizing a skeleton in mind.