Open the Google Doc
Right-click the image
Select Save to Keep
Open the Keep note in the sidebar
Right-click the image in Keep
Select Save image as
Choose a folder and save the file
If Save to Keep is not available
Click File
Select Download
Choose Web page (.html, zipped)
Open the downloaded ZIP file
Find the image in the extracted folder
Copy or save the image file
If the image is in Google Docs and you need a quick copy
Right-click the image
Select Copy
Paste it into an image editor or document
Save it as an image file