I just ran into a gotcha where the url http://thegenericman.com/assets/img/product_images/tgm large/GNRCMAN_122211-739.jpg (i.e. with a space in it) was failing due to cURL not normalizing urls, and hence pulling in the wrong file. I'm aware that this url is invalid, but actually fixing it is out of my hands.
Why cURL does not handle this itself is discussed here.
Normalizing the above url to http://thegenericman.com/assets/img/product_images/tgm%20large/GNRCMAN_122211-739.jpg resolves as expected.
Just a heads-up for anyone else that may run into mysterious failures.