When you add an image to a layout, the Picture Properties allows you to specify a simple path from Data Driven Pages. This allows the image to update based on which ever page you are looking at.
Setting it up and browsing through the pages works perfectly fine. the images refresh with no problems. However, when you export multiple pages to PDF, the image is blank on every page. After the export is complete, the image will be blank in your MXD even though the path is still defined. it works if you print one page at a time but that's not a feasible solution for thousands of pages.
I have tried it under different installations of 10.2.1 so it's not isolated to a single machine. I've tried it from new MXDs and the problem still occurs. I've also tried it manually and by Python outside of ArcGIS Desktop and all end with the same result.