How to import image from scanner/printer in writer .odt document or calc .ods document
In general you select the to be used device in Insert > Media > Scan > Select source. And in next step you use Insert > Media > Scan > Request. But details depend on operating system, scanner and installed driver. Please edit your question and add these information.
My preferred workflow is to scan to a folder, edit the image in graphics software and save in my preferred format (and number of colours, transparency, etc), import image into LibreOffice.
This way: one trip to scanner, image is best possible, format of image in LibreOffice is my choice.
Otherwise, as Regina says