I am using the imagecache_external module to set the size of images from external urls. For some reason, some images are displayed and some are not. The all have the tag structure of
<image typeof="foaf:Image" src="http://[path]/sites/default/files/styles/thumbnail/public/imagecache/externals/50fda6daf05096f6b200b2a054a38084?itok=cHTsorEg"
but some are just blank images. I know that the external image is valid because when I display it in a normal image tag, it works fine.