There is a 20MB size-limit for each file you attach to your ticket.
Here is how to attach a screenshot for iOS devices:
If the paper clip does not react on your device: Go to Settings > Privacy >Photos > Cradle of Empires and turn on All Photos or Selected Photos access. If you choose Selected Photos, you will need to edit setting Edit Selected Photos each time you need to send us a screenshot. Then open Settings > Privacy > Camera and turn it on for Cradle of Empires.
Here is how to attach a screenshot for Android devices: