save_image(img1, 'img1.png')
Here, you are saving the img1 as img1.png in your current working directory, that argument is actually the path where you want to save your file, you can pass anything like folder1/img1.png in that function as an argument if your file structure looks like this, then the img1.png will get saved in the folder1.
current_working_directory
|__folder1
|__file.py