Hate to bump old threads, but I'm getting this exact same issue. No mods or anything else installed, just a flat 4.7 build 3106. I've uninstalled/reinstalled to no avail.
Seriously though, I've had multiple Subsonic servers over the past 2 years, and on all of them I kept for more than a few months, eventually the image search stops working.
Very early on in 4.6 this worked, but it hasn't in a couple years. I just installed 5.1 (build 4340) on a new box and it still isn't working. Just hangs.
It's not a routing issue; I can get to google images just fine from the box from a browser.
Not sure about you guys, but for me it ended up being an ad blocking issue. I use(d) Ghostery, and it was preventing the frame from loading the images. Once I whitelisted my IP/domain, it worked again.