iMessage Contact photos not showing on Mac

It's likely just a glitch while syncing across devices, so let's try some troubleshooting.

Go to your iOS device and (Assuming you're on iOS 13) go to Settings>Apple ID>iCloud>Contacts, turn it off while keeping it on the device, and turn it back on.

Then, proceed to do the same thing on your Mac. I'm assuming you're on the latest macOS Catalina, so the instructions might be slightly different if you're not. Go to >System Preferences...>Apple ID>Contacts and turn it off and on again.

Restart both devices, unlock them and wait a couple minutes. Let me know if this fixes your problem or not.

Sorry for the late response. You might wanna take it into an Apple Store, they'd be able to take a better look at it there.