This hack is fantastic! I have a mix of both vertical and horizontal aspect images, so my filmstrip looked kinda jacked up, so I set my images as a background image (set to cover) so I could have consistent size thumbnails.

The only problem here is the placeholder image shows up on top of the background image. So I just created a transparent placeholder PNG and uploaded that as the image in the Image Properties section. Works like a charm!

Thanks so much for sharing this!