You can either export the proxy from PFTrack, or you can use an image editor. I like XnView because it supports pretty much every format on the planet.

Download it, go to where your images are, select all of them, and go to Tools>Batch convert. Go over to actions, and click on the plus button under processing, then image, then resize. Set the width to 960, and the height to 540. Then, go back to output, and enter "{Filename}" as the file name. Choose your format (jpg is fine) and choose a new directory to save the images. Click convert, and it will run through all the images in a few moments.

Even though you might have hidden the image plane, it still might be hanging around in the hypershade, so it's best to just use it, but put in a proxy. Just open it up, and point it to the new proxy location, and it should go faster.