Unfortunately, Google Docs doesn’t allow downloading of images from your documents.
However, Google does have a free add-on available. Go to this Image Extractor weblink, click the blue free button, and a Google Doc page will open requesting your permission to run.
Please note: you will need to have your images set to “in line” for downloading. Once you highlight your image and click the blue “Download Image” button, your photo will be saved to both your local computer’s downloads folder and your Google Drive.
Also published on Medium.