This app was mentioned in 19 comments, with an average of 3.89 upvotes
You might try Micopi Free It auto generates a unique image for all of your contacts that don't already have a picture.
I once found an app that changed all the contacts photos to a first name last name letter combo and added colours as background. I'll try to find it.
Micopi: https://play.google.com/store/apps/details?id=com.easytarget.micopi
I had to run it a few times before it actually worked. It takes several minutes if you have lots of contacts, and it seems to get messed up if your device goes to sleep while it's going through its process. But it worked eventually, and the results are nice.
I kinda like Micopi, to give my contacts without a picture something unique.
It also on the Play Store
It's the profile pictures for those contacts. I had an app years ago, that procedurally generated profile pictures for people lacking them based on the contact name. Looks like it has a lot more variation now a days too, I haven't looked at for years.
https://play.google.com/store/apps/details?id=com.easytarget.micopi
You could use this app. It's called Micopi it can either entirely do your contacts or just what doesn't have a custom image it fills them in with a slightly cooler looking bubbly image!
I don't know if this is what you're looking for, but Micopi is a great app for generating a unique image for each of your contacts.
Micopi is a similar app.
I've personally used Micopi.
Micopi Pico is useful if you're on Android. It generates a pretty pattern for all your contacts that don't have pictures.
Try Micopi: https://play.google.com/store/apps/details?id=com.easytarget.micopi It should be able to overwrite your existing contacts picks and gives them a pattern instead.