Profile > Edit Profile > Privacy
p.s. I can't blame you for not being able to find it as it's not easy to find as a while ago I was struggling to find it myself.
You can block individual avatars with uBlock Origin. everyone should be running that uBlock Origin (by Raymond Hill) extension in their Chrome/Firefox browser as the internet sucks without it. it blocks a lot of random junk online and makes your browsing experience more secure. uBlock Origin should be a default install for everyone!
but with uBlock Origin you can flat out block someones entire avatar section or the individual avatar itself etc by clicking the uBlock Origin icon then select 'enter element picker mode' (the icon that looks sort of like a eye dropper) and then move your mouse pointer over the section you want to block as it will show you what it will block and then left click once you highlight what you want to block. if you mess up you can remove the thing you blocked by going to uBlock Origin icon, then select the 'open the dashboard' (which is the icon with the lines on the right), then go to 'my filters' and remove the entry there and click apply and your good.
basically if you block the entire avatar section of a individual, even if they change avatars it won't show up. but if you just block the individual avatar itself, if they change avatars, their new avatar will show up. you got to watch what you select as that determines which one it blocks.
here is some screenshots on what I mean with uBlock Origins 'element picker mode' using my own avatar as a example...
to block a specific image...
to block someones entire avatar section from showing (which means even if they change their avatar it will automatically be blocked)...
if you have not noticed, the key thing here is what's highlighted in the red square! ; once you highlight what you want to block simply left click and it's gone
NOTE: you can also use wildcards to like for example.... websitenamehere/randomnamehere/picture.jpg ; you can block that or if you wanted to block all images to that general link section you could do... websitenamehere/randomnamehere/*.jpg ; doing that would block any images linked like that so it would not matter what the 'picture.jpg' was named as, it would be blocked. like picture1.jpg or picture2.jpg etc etc, all would be blocked.
p.s. I don't blame you on blocking some avatars as I do the same