There is NO WAY you can legitimately authenticate anything just by looking at a PICTURE.
As an authenticator, I'll comment on the first sentence of your post.
While there are some "5-star," "AAA," "mirror image" fakes where in-person inspection is necessary for authentication, there is absolutely no question that
most items can be authenticated from pictures (plural)-- NOT a single picture as you've stated. A good brand expert knows what to look for in construction, hardware, markings, patterns, date codes, serial numbers, linings, stitching, etc. An experienced authenticator has a library of thousands (or tens of thousands) of pictures, notes regarding what they've learned over the years, exceptions to various "rules," etc.
Additionally there are cases where an obvious fake can absolutely be authenticated (or rather, un-authenticated) by looking at just one picture but I would never consider something authentic if I were shown just one picture.
I made the mistake of trusting a seller on Tradesy, who provided a "certificate" from AutheticateFirst. This was my first real designer bag purchase. I blame myself, ultimately, for being so naive and thinking that I could trust any company that claims YES this is real or YES this is fake over a picture of a bag. You have to physically look over a bag IN YOUR OWN HANDS and study ALL of the details before knowing the facts. You can't see up-close stitching on a picture! I emailed ***************** to find out their process but was given a BULL**** answer and was told "do your research". I responded by saying how can I compare the pictures they received to my bag, especially when the ID tag on the bag came out way too dark on the "certificate" they provided?! Their response to me was, "You are wrong but entitled to your opinion." Nothing like passive aggressive treatment from a business!! DO NOT TRUST A COMPANY LIKE THIS!! I have learned the hard way.
I don't know whether you're a buyer or a seller so I don't know whether you bought a fake or were accused of selling a fake. I also don't know the brand of the item you are discussing so my comments are generic. (ETA: I just realized this thread is in the LV sub so I assume that's the brand.)
I'd like to think that more than one picture was submitted in order for a judgement to be made.
I would hope that there'd be some information as to why the item is fake or authentic because generally, ebay, paypal and c.c. companies don't accept one word determinations when deciding disputes. They like to know the reason the authenticator determined the item to be as they deemed.
If you aren't happy or if you dispute the finding they made, you can always post pictures in the appropriate "authenticate this" subforum here or you can get a second opinion from another professional service.
But again, the main purpose of my post is to say that with the correct clear pictures, correct angles, correct lighting and correct details submitted, items CAN be authenticated from pictures. 
