I think you've hit the nail on head OP. You miss him, when you are out. So a little snapshot for a brief second is lovely. Maybe it is an Instagram moment, mental or real image, but hey if it keeps OP happy , so what? It's not unusual to miss your child and feel comforted by a photo on your desk, phone or brief text.
I'd prefer to hear, "yes they're great, just been drawing and down the park, enjoy your meal" or "Littlebed is tired & snotty so we're snuggled under blanket watching Barbie" than "fine, don't worry". It doesn't mean I don't trust my parents (if they are visiting to look after youngest DC) but that, every now and then, when I've stopped between cases, I often think of my DCs and it's so nice to imagine what the youngest is doing. I'm a working single mother, doing slightly shorter hours to see DC more, who rarely goes out unless with or for my DC.
I never get updates from childminder until pick up but she will say 'oh if weather is good, we're doing this today' at drop off, which I equally like. It makes me happy at work to know they are having fun, to slightly picture it or get excited for them, and it easier to share stories on drive home.