These are some pictures dating back to 1996 from the beta version of StarCraft - go to www.star-craft-2.com for more beta snapshots and information.
Click here for rumor photos from SC2
(Above) Picture from the earliest designs for SC; overlords could attack and had shields...
(Above) All units used to be outlined like the dropship above when selected...Also notice that the dropship had a different portrait and could hold up to 8 goliaths.
(Above) Notice the hydras have claws and use melee attacks.
