The pic shows she attaches it to the metal hardware on the handles like I do with my mono classic 25. (I believe, at least..)
I don't recommend doing this with a Speedy larger than the 25 and not because of concerns of damage: but, because when worn on the shoulder that way, it twirls around (the end of the bag could swing away and hit your body and then start the twirl), and, also because if you try it crossbody, the strap ends are anchored closely together but the bag is much wider and then you look like you've got this big thing jutting out from you when the straps are hugging your body more closely, instead.
I do have to note that my strap is an older vachetta strap and so is my bag. Since everything (hardware, leather, etc) is old, I'm seeing that, over time, the part of the leather that's on the outer edge of the chaps where the metal part of the handles to which I attach my strap are -- are beginning to show signs of the metal rubbing. I'll attach a pic to show you what I mean. Newer bags and straps probably won't have this problem.
Also: about opening the bag -- you have to probably attach diagonally like I do -- which means ONE of the straps will get in your way when you want to unzip the bag completely (get in the way at one of the two ends depending on how you anchored). You have to be okay with this.
However, the advantage of anchoring on the handles is that it keeps the entire zipper area poofed up and straight allowing you to unzip a bit more easily with one hand. For me, the strap that gets in my way is the one toward my back and I can unzip with one hand about 2/3 of the way before my hand runs into the strap -- but that's enough for me to reach in and grab my wallet. For those Speedy B owners with bag sizes 30 and above, you'll know what I mean when I say the closed zipper folds a bit when your bag isn't very full and you have to straighten the thing before trying to unzip a side or it won't want to unzip.