Right after the shot of the Falcon blasting out of Mos Eisley, the first shot of Solo back in the cockpit has something interesting. On the left-hand side of the screen, in letterboxed copies, someone (it looks like Ben’s shoulder) is walking down the corridor seen through the open door behind Han.
What are garbage mattes? You’ll know it when you see them. They’re the grayish-yellowish squares or rectangles that surround a ship (usually TIE fighters) in space. Although bluescreens are used to separate a ship from its blue background and place it into its appropriate background plate, there’s often a lot of extra clutter on the edges of the bluescreen that have to be removed: lights, support rods, and even technicians. So to separate the bluescreen from the set, additional pieces of opaque film are "animated" to block out everything else. The outlines of this film are what cause the garbage mattes. When viewed in the theater, these things don’t really stand out, because they are subtle changes in the black starry background. But on video, that doesn’t reproduce black very well, they stick out like a sore thumb. The THX copies have cleaned this up quite a bit, and letterboxed copies reduce the size of the mattes. Special Edition does away with them altogether. In this case, the two Star Destroyers pursuing the Falcon have visible garbage mattes.
The interior cockpit set of the Falcon does not match the exterior of the miniature. The number of windows and bands change. This would be corrected by Empire.
Chewbacca took off his bandoleer right? Well, when the Falcon jumps into hyperspace, he’s suddenly wearing it. And Han has suddenly taken off his gloves.
When Tarkin demands to know the location of the Rebel base, it cuts from a close up of him to a reaction shot of Leia. Tarkin's dialogue continues through the cut, but the lip sync is off during the shot of Leia.
Alderaan has a strange fuzzy halo that is really its matte line showing up on film.
The airbrushed flash of the Death Star's laser is off-registration in this shot. It doesn't line up with its background (look at the gunners' helmets and outlines). Incidently, these gunners are actually ILM crew, Joe Johnston and Steve Gawley.
The close-ups of Artoo during the holochess games must be stock footage from another part of the film. The lights reflected on his domed head are the vertical striped lights from the Death Star.
As Vader says, "I told you she would never consciously betray the Rebellion," he ends up pointing a lot longer than he does speaking. David Prowse is notorious for over-pointing. Check out the Jerjerrod opening scene in Jedi. That finger’s everywhere!