Straight out of the MM? No, too many players instantly know what even rare monsters are. If I want to show a picture I do a little online searching and it is pretty easy to find some pinterest drawings out there that work for most monsters.
Also for some monsters there are much better pictures available than what is in the MM. The very first time the party encounters a balrog do you call it a balrog? No. Do you show them the picture from the MM? No. You use your tablet and show them with the volume at max a clip of the balrog first coming into full view from "Fellowship of the Rings" of course. ;-)
I do at times, though as previously mentioned the picture if in the MM players know exactly what they are confronted with, of course I only had to change up the creature once that they no longer trust the picture.
Since my group is scattered to the four winds and thus always have to use roll20, yeah I almost always make tokens with the monster artwork on it. Likewise, when the players have a particularly noteworthy encounter I add it to a running "Hall of Infamy" that has the full artwork with a retelling of the encounter beneath it. It has proven to be surprisingly popular to flip through the highlight reel sometimes, especially since the campaign has been going from level 1.
I would generally prefer for them to use my description of the monster to create their own image. Their minds will fill in details for certain adjectives like imposing, beautiful, grotesque, pustulent, elegant, brutish, sexy, and dreadful. Because it's their minds creating those details, they'll concoct an image that's personal to them and will therefore be more accurate to those descriptiors than I would be.
It's a lot like a horror movie not showing the monster because nothing is scarier to you than what you imagine to be scary.
However, I will show the picture if they really want to see it, or if they feel the description is vague or confusing.
Nah. I like to describe common MM monsters basing my descriptions on 1e illustrations.
"You follow the sounds of the crying peasants until you come to the edge of the woods. Hiding in the underbrush you look across a clearing to a small village made of primitive huts, beyond which rises a mountain with a large cave entrance. You see pig-headed humanoids wearing simple mustard-yellow tunics and pants, carrying spears and simple wooden shields, parading a group of terrified peasants through the village towards the cave. They have brownish skin that has a blue sheen, as if oily. Their pinkish snouts and ears standout.
My dad shows the group pictures of the monsters being encountered. Me? I like to describe their appearance, no pictures needed.
This led to a somewhat humorous moment a few sessions back with our new group:
Dad: "two small figures run along the side of the cliff towards you. They are kobolds."
New Player 1: "what's a kobold?"
Me: "It's like a cross between an anthropomorphized lizard and a pit bull."
New Player 2: *chuckles* "anthropomorphized lizard-dog."
Dad: *holds up Monster Manual*
New Players 1 and 2: *look at picture, then over to me* "it does look like a pit bull-lizard-man!"