The URL field in the ImageField is ReadOnly, so you cannot write it. You should probably use in addition a URLField (better than a CharField) to save the URLs.
You can allow null values on both and use only the appropriate one according to your scenario.
I have Django model with Image field, but sometimes I don't need to actually upload file and store path to it, but I need to store only path. Especially url. I mean, I have web client, that receives both foreign urls like sun1-17.userapi.com and url of my own server, so sometimes I don't need to download but need to store url. Is it possible, to store url in ImageField, or I need to make CharField and save files via python? If its impossible, how do I save file in python3, having one, sent me via multipart?
How to save URL to a Django ImageField