PdfTrick is an open source application for selectively extracting images from one or more PDF files.

Launch the download (it's Java-based, no installation required), drag and drop one or more PDFs into the program and their page thumbnails are displayed in a sidebar.

Clicking any page displays thumbnails of the images it contains.

Select one or more of these images, click "GET IMG", choose your destination folder, and the images are extracted and saved. (Actually they're saved to a PdfTrick_dd-mm-yyyy_hh.mm.ss subfolder, which is bizarre and slightly annoying, but you'll find them easily enough.)