I don't know about the propped up corpses in old western photos, but yes it's Egyptian, it prepares and protects the soul into the afterlife, the end of one journey (the mortal one), the beginning of the next (the divine one) . It's the original alpha and omega. Beginning and end. The X is the original alpha/omega symbol.
The skull and crossbones are usually femurs crossed , and has many meanings thru history, even one as "good luck" or even "safe passage" but it basically is the Chi Rho symbol, from constantine (under this sign we shall conquer thing), but it goes back even further. the strange looking P with an X over it symbol, which are Greek as well as Phoenician in meaning. It later became a symbol for Christ, and even John the baptist , as well as Templar symbol used in battle. The Chi is cross (X) and the Rho (P) actually means "Head". Again the X is really the alpha/omega symbol and you will see the Alpha and omega added on the sides of the Chi Rho alot. Probably a several meanings I missed, but whats funny is there are so many meanings of it that the people who used it wouldn't have known the what an original or true meaning of it was. So an original meaning probably can't be found on it, but I suspect it was somehow derived from the Egyptians as well, especially with the safe passage meaning.
