Minecraft wiki entry for Head, associated text: Block entity data
Tags common to all block entities[show]
 ExtraType: Name of the player this is a skull of. This tag is converted to SkullOwner below upon loading the NBT. When loaded sets the name to the value and the UUID to null.
 SkullOwner: The definition of the skull's owner. When this is a player_head or player_wall_head, shows this player's skin; if missing, shows the head of the default Steve skin.
 Id: UUID of owner, stored as four ints. Optional. Used to update the other tags when the chunk loads or the holder logs in, in case the owner's name has changed.
 Name: Username of owner. If missing or empty, the head appears as a Steve head. Otherwise, used to store or retrieve the downloaded skin in the cache. Need not be a valid player name, but must not be all spaces.
 Properties
 textures
: An individual texture.
 Value: A Base64-encoded JSON object.
 isPublic: Optional.
 profileId: Optional: The hexadecimal text form of the player's UUID, without hyphens.
 profileName: Optional: Player name.
 textures
 CAPE: Optional.
 url: URL of a player cape (64x32 PNG).
 SKIN
 url: URL of a player skin on textures.minecraft.net.
 timestamp: Optional: Unix time in milliseconds.
 Signature: Optional.