This option is to allow you to change the source of where your images are coming from. It allows you to choose from Arcade Database, theGameDB or Screenscraper.

Screenscraper offers more options for game scraping (for example several image options, you can scrape video previews, etc.). But there is also a limitation in the number of assets you can download each day: 50,000 requests max per day. Also, if you use a “mix” for the image, be aware that you need to download a screenshot + box + game title/marquee, which are 3 downloads for 1 composite image.

In order to use Screenscraper, you need to create a login on their website (otherwise you'll get a message in French telling that you need to register an account there).

Is there any way you can launch scraping from the command line, like other retrogaming distributions? No, scraping is part of the EmulationStation binary, and can be only started from there.

I have a very complicated ScreenScraper password, where can I copy/paste it rather than using the EmulationStation keyboard? You can edit /userdata/system/configs/emulationstation/es_settings.cfg and edit the section:

      <string name="ScreenScraperUser" value="your_login" />
      <string name="ScreenScraperPass" value="your_pass" />

Make sure EmulationStation is stopped before editing this file, otherwise, ES might reverse your modifications. If you're not sure how to stop EmulationStation before editing this, you probably should use the UI to enter your credentials