I have following input
\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAA7YAAAISCAIAAAB3YsSDAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAA5JxJREFUeNrsnQ
This question looks like it should help: Django - how to create a file and save it to a model's FileField?
You should be able to decode the base64 string and supply that as the content argument to FieldFile.save:
content