This wonderfully useful feature, done through offsite images (i.e. hotlinking), deserves two comments:
It is NOT bandwidth theftHotlinking, placing an image from one site in a second, unaffiliated site, is sometimes regarded as an impoliteness and even as theft (it takes unfree bandwith from the first site for you to see the image). While this may well be true in some cases, we disagree it is in our case. We believe bandwith prices have fallen down enough for us to deserve full-size images as a preview to your website. If we like what we see, then we will enter your website and explore it (and click on your ads and buy your stuff).
There are several ways to prevent hotlinking and Imagery is not immune to any of them (yet); this is a common reason why some pictures fail to load and can be easily remedied by going directly to the image source-page.
It may need a quick tweakYou could have Firefox configured to load only images from the originating web site and if you do, you wouldn't be able to see a single image inside Imagery. Fear not, it takes only a checkmark to solve this. (Thanks to John Law for the heads up.)