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The first is the Hobbits from "Lord of the Rings": Elijah Wood, Sean Astin, Billy Boyd, Dominic Monaghan. The first thing that tipped me off about this one was no certificate of authenticity: I got this one as a gift way before I started getting "serious" with autographs. Now, comparing it, the Sean Astin and Billy Boyd seem a little off while the Dominic Monaghan and Elijah Woods seem a little "crazy"... not a whole lot like what their signature looks like.
The next is Alec Guinness. It's purchased from a UACC dealer with a certificate of authenticity, and I really can't tell whether it's authentic or not. It's right on the cusp for me, largely due to the bleeding ink used for the autograph, which makes it hard to make out individual characters that would have been clearer.
The final one is a Natalie Portman. Before anyone starts saying how she never signs index cards anymore, or anything that neatly, this was purchased from a very reputable person, and it was signed before the big "Star Wars" craze swept in, while she was still fairly young. There are certainly characteristics of this autograph that match her current autograph, and I know it would be hard to find anything to compare it with, especially before she really became famous. I'm pretty sure this is authentic, but any opinions are welcome.
Basically, I've already got some ideas about the authenticity of these autographs, I'd just like some solid backups before I display them prominently or get rid of them.
As a side note, I'm almost 100% sure this "Harry Potter" poster is not authentic, since its origins are quite questionable and the signatures don't match their authentic counterparts, but it was a special gift for a birthday, holds special meaning, and looks great, so I'd like to be doubly sure before it's confined to the closet (it's "signed" by Daniel Radcliffe, Robbie Coltrane, Maggie Smith and Richard Harris).
Thank you all for any help you can give!