To gauge weight by picture, you need a pic taken of the side of the dog standing properly (not bunched up). And then you need an overhead pic. <- You can't gauge a dog's weight with them sitting all bunched up in somebody's lap.
The sideways pic looks at the outline of the dog - and you want to see a tuck. Doesn't mean a dog isn't overweight if you see a tuck, but you want to see a tuck there (if a lot of feathering, you can still go by the dog's jacket I think, or regardless that's where you do a hands on check). If there is no tuck, that means the dog is obese.
The overhead pic looks for a waistline (behind the rib cage). If it's pretty much a straight line from the widest part of the rib cage to the hips, that's a sign your dog is overweight. If there is a swell or bulge right there, then your dog is obese.
Feeling for the rib cage - I think hotel4dogs kinda opened my eyes when it came to that, as I've always just felt my dog's sides. But you really are feeling from the top of your dog's back. I guess with your hand flat and with light pressure with your fingers on either side. If your dog feels pretty solid up there, then he can lose a few pounds.
I'm hoping to control Bertie's weight gain over the next 2 months and ideally he should be 60 at 6 months. I think Jacks was at the same point and touched 70lbs by 12 months. Which was the point when our vet saw the weight on the paperwork and came storming to the room fully prepared to scold us until he saw Jacks. LOL.
With Bertie, I'm sure it's going to be interesting because he's been gaining 5-10 lbs every week. And he's 35lbs at 3 months. And I've been keeping him quiet as far as exercise the last few weeks because of ice on the road, so he is not as muscular as Jacks was at the same age.
ETA - I forgot to say, but if your dog is over standard (I think you said that Bentley is full height? Or getting tall), then you can't go by the weight on the standard. You have to do the picture/hands on check. So I wouldn't freak out too much about the weight on the scale alone and compare it to average sized goldens. With Jacks and his thyroid issues (at his heaviest he got up to 85lbs), I do monthly scale visits at our vet. This is the best way to control your dog's weight, because instead of suddenly having to get your dog to lose 30lbs, you may be looking at only 5-10lbs. And with a 6 month puppy, I wouldn't go too crazy because he is probably still growing.