I can't seem to get image previews to work correctly in Statamic. I created an asset container and added images to it. I can see the assets under 'Content', but I don't see any thumbnail previews, just tiny white squares. When I double-click an asset, I see it just fine, but there's no preview in the assets list. I also don't see a preview when I add the asset to a collection item. The images are displayed in the output as expected. The image manipulation driver is set to 'GD'.
Any ideas on how I can get the image previews to work?