When syncing with an iCloud account the contacts image is not downloaded to the device.
One must still have chaos in oneself to be able to give birth to a dancing star. – Friedrich Nietzsche
I have added a check: https://gitlab.com/bitfireAT/davdroid/commit/20ee4e03f3196c17745961f25a12301818411452
With calendar birthday adapter app it works
Please follow up in #48.