For the most part, Atticus will typically import the images you have already added to your docx upon upload. As long as those images were added in a 'traditional' manner in your original docx (for example, by the option to insert an image that you upload from your computer), they should upload with no problems.
Do, however, keep in mind that if the images in your docx file are particularly large image files, they could cause a timeout process during the upload that might prevent the file from making its way into Atticus at all. You'll just want to make sure that the files aren't extensively large to begin with. Also, most changes that have been made to the image in Word will not carry over to Atticus since both systems have different ways of handling image settings.
We recommend saving images separately and importing your manuscript without images, then inserting the images directly into Atticus instead. You can learn more about importing images directly to Atticus in this tutorial: https://www.atticus.io/interior-book-images/