Why are images noted as Temp status in URLs

I am noticing that in the Link embedded image field  in the Edit Image window that the URL looks like this:  www.example.com/.../filename.jpg

Why is the status temp?  Why does it say default-source, and WHY does it appear as a crawlable image when Google-bot (or other bots - I've tested two) scans my site?

Should I just block these in our robots.txt file?