Also works with iPhone contact entries.
Probably also with Android, but I can’t test it myself.
If I add an image to my contacts from the IOS world, this is also visible in the Outlook client.
So the image is definitely synchronized.
I also see contact pictures on the tablet or smartphone when I add them using Outlook.
SoGo also displays the images. You just can’t change or remove them.
At least I haven’t discovered the function yet.