While some clothing brands are often faked (think fashion brands such as Gucci and Burberry), my experience is that tailored men's brands are seldom forged, and when they are, they don't even come close to the real deal because it's not a very lucrative business for forgers. In this case, the hand-sewn label along with the signed lining, as well as some of the subtle details I see in the construction, make me pretty confident that this is the real deal. So in short, it is very possible to authenticate tailored garments from a few images.I've seen a number of similar requests to authenticate an item of clothing from noted manufacturers like Brioni, Zegna et al. And I understand the need for an evaluation when one is thinking about buying something online, based on pictures and descriptions. It's just that I'm not sure how well anyone, even an expert, can do this without physically handling, and looking at, these items. This is especially true when the item does not have any obvious departures from the authentic cut or style. There is a lot of information in the hand and texture of the material, and the movement of the garment while one is wearing it and moving about, that is critical to correct identification. And labels, of course, can be faked, or genuine labels sewn on inauthentic garments.
I have had a fair bit of experience in the authentication process as a collector of other objects. To draw an analogy or two, you would not want a rare book or rare stamp (I collect both) to be purchased without some form of authentication by experts. In the case of philately, you would send the stamp to an expertizing service, of which there are several, or else see if the item being offered comes with such an evaluation by an expertizer -- a certificate of authenticity. There are also technologies that can reveal forgeries and fake postmarks and cancels. In the case of books, both provenance and the reputation of the antiquarian bookseller are important, as is a photograph of the copyright page, which is rarely faked or duplicated. I would never purchase a very expensive rare book from an unknown seller on an online site without some way of authenticating it, and often the onus is on the seller to provide such verification. I point these things out to emphasize the difficulty of real authentication based on a couple of photographs viewed on a computer monitor -- or perish the thought, on a tiny cell phone screen, LOL.
Lastly, while I have not heard of clothing aficionados collecting fake clothing, it is not at all uncommon in philately to collect forgeries. In fact expertizing organizations often have collections of forgeries because they help in identifying the real thing. For example, as a member of both the American Philatelic Society and The Royal Philatelic Society of London, I can attest to the fact that these organizations have excellent collections of forgeries and outstanding expertizing services -- they do come at a cost, though. And some collectors find forgeries qua forgeries collectible!
I guess I'm a sort of "expert" on certain garments. I made a living for a couple of years buying and selling high-end menswear so I have a good eye for it. And, while I have several Brioni suits of my own, I've never bought one brand new so I know what hallmarks to look for to spot authenticity. But you are correct that the best way to gauge the authenticity of anything is to inspect it in person. And even then, there are good counterfeits that will fool everyone except the most well-trained set of eyes.That's good. I'm glad you are able to authenticate this garment, and perhaps others like it. I would definitely call you an expert, and what you do as expertizing. This is similar to what I would do with my rare books and stamps. Although I am reasonably confident of my judgment with books and stamps (and I do have books and reference materials to assist me), I would still defer to expert opinion, especially when the value of the item is high. I would not trust my judgment alone when it comes to a stamp worth, say, $10,000, or a book valued at $5000. I would seek an expert. I'll keep you in mind, my friend, if I have a question about clothes -- although most of my purchases are vintage items these days, and not the fancier Italian brands, LOL.
A digression. During WWII the Germans picked out some talented counterfeiters and brought them to the Sachsenhausen concentration camp, and gave them good food and other amenities in exchange for their skills. These chaps produced counterfeit banknotes of pounds sterling that the Bank of England's experts could not tell apart from the real thing! It was called Operation Bernhard. There was a great film made of this in Austria,called The Counterfeiters, which we discusses in the film class I teach for retirees.