how to make a difference when creating a new animal and editing an animal. new animals don't need pictures, edit animals need pictures?

how to make a difference when creating a new animal and editing an animal. new animals don't need pictures, edit animals need pictures? the data type field for the image is XFile

the data type of the field for the image is XFile, which cannot be empty. if i add manually it will not good or if forced how i fill it?