If you want to serve retina images with WordPress plugin WP Retina 2x but you’re using bfi_thumb, you’re going to have a slight problem.

bfi_thumb creates new file names that are not picked up by WP Retina 2x. For example, you may have an image file called your_image.jpg and WP Retina 2x may have prepared another called your_image@2x.jpg to serve on retina devices. But when you bring bfi_thumb to the party as well, it’ll create it’s own file e.g. your_image_resized.jpg. When your page is loading WP Retina 2x sees your_image_resized.jpg, it doesn’t have a retina-equivalent prepared.

I overcame this on my site by making a modification to bfi_thumb so it creates two resized thumbnails: your_image_resized.jpg and your_image_resized@2x.jpg. You can check out the code on Github.