The Special Edition replaces the sky with a much more interesting-looking dusk. The live action plate is also color-adjusted to match.
The RA-7 is a line of low-intelligence servant droids, often owned by Imperial officers and nobles. Often used as simple menial labor and "house-keeping."
Serv-O-Droid/Delban Faxicorp's CZ-units are outdated communication droids used in business. This droid was actually an early design for Darth Vader’s armor (see Art of Star Wars, page 49).
R1-G4 is an outdated astromech designed for use on large transports and capital ships. This large dark droid was left behind on Tatooine by its owner. It uses a Mark II reactor drone radiation-shell.
R5-D4 is from a failed line of astromech droids. Industrial Automaton's cost-cutting made the R5 very unpopular. To recoup loses, many R5 shells were urned into agromech droids and sold in the Outer Rim. R5 is a bitter droid who purposefully blew his motivator to keep Artoo and Threepio together.
WED15-I662 is a typical Cybot Galactica "treadwell" droid. These droids have multiple appendages to repair heavy machinery and vessels. Luke had a treadwell similar to this one in scenes cut out of Star Wars.
Power droids are ambulatory power sources. They have limited cognitive
functions. This particular model is a Veril-Line Systems EG-6. It has been
memory wiped and has no knowledge of its identifying serial number.
During the sandcrawler sequence, Artoo's legs are on backwards. The detail on his shoulder joint gives this away. Note that when he is in the Lars garage, his legs are in the correct configuration.
First, quick psychology lesson. Closure is when you think you see something, therefore you see it. Like people who swear they see strings holding up movie models when there are none. Well, in the sandcrawler sequence, right before the shot of Treadwell, Artoo swings his head around, and you can see right into his eye. It looks like you can see Kenny Baker’s face.
The M-HYD unit is a droid designed for hydroponic operations. This pretentious unit knows several languages, but prefers to converse in binary.
As Threepio shouts "It is you, it is you," right by his screen-left elbow is another golden 3PO unit, with its head smashed in. You can see it quiet clearly in the letterboxed copy and in a still in The Star Wars Storybook.
The Special Edition replaces the dark blue sky with a darker sky, and adds several stars.