signaturefield and private file system

I'm trying to use signaturefield on a D7 site with private file downloads. The module works wonderfully for collecting signatures in a webform and generating the signature image appropriately in the correct location for the private file system. However, I'm getting access denied messages whenever I try to view the images. It seems as though the private file system doesn't know what to do with these images. I'm currently trying to read up on the file management APIs to see if I can help figure out a way around this.