When you have images inside a Google document, Docs doesn’t allow you to extract the image directly from within the document editor window, which is a pity; sometimes it’s handy to be able to download such images. Luckily, there are a few workarounds.
Firstly, you can first publish your document as a web page (as described in this previous post), then download the image from that page while it’s displayed in your browser. Use the blue Share button at the top right of the editor, then select Publish on the Web.
Open the supplied link in a browser and download the image as you would do from a normal web page. (Note: you may find you have to sign out of Google first).
An alternative method of extracting the images from your document is to download the document to your own computer. You can download the file in various formats including .docx, .html, .odt or .pdf.
Once you have the document stored locally, you can use the relevant application to extract the images. Note that if you download in the zipped HTML format, the download archive will contain a folder called images with all the image files inside.