Tiberius' painting looks like this, and the two of you have presumably used the same 'great all of china' reference image, if (as you say) you didn't take it from here:
Most images on google are copyright, which means you can't use them for commercial work OF ANY KIND. A practice image obviously isn't commercial work, but it gets a bit wooly if you then use this in a showreel, and it breaches copyright entirely if you then (for example) sell it as a print on your site.
Sites like morguefile.com, sxc.hu and others have completely free images, and flickr has a subset of 'creative commons' images, some of which you can use for commercial work.
But really, really don't use the work of other artists - even for practice. It isn't actually good practice in any case, since they've done a lot of the work for you.
Hope that clears it up a little?