The only way I've worked out how to even save Instagram images locally is using the page information (ctrl+i) Media tab in Firefox and sort through it to find it there. Terrible for an image hosting website.
It's not an image hosting site, it's a social media site whose goal is to keep you coming back for more. The easier it is for you to save their content locally, the less likely you are to spend as much time on their site.
If you're running Windows, though, you can use the Snipping Tool to grab the part of the screen you want to save, which may or may not have an image in it.
They started replacing the default screenshot tool with snipping tool, but maybe it's not the default to call it with PrtScr
Saving from source was in context of saving from Instagram, I find screenshooting Web pages less fitting than getting into the source of the page, albeit the former is simpler
Ah, gotcha. I never screenshot for stuff on the web -- like you said, you can just save the image. I take screenshots when I'm playing Civ succession games.