{{Double image stack|left/right/center|Top image|Bottom images|Size|Caption|[Bottom caption]}}
{{Double image stack}} creates a box with two images stacked on top of each other. It needs parameters like this:
{{Double image stack|left/right/center|Top image|Bottom images|Size|Caption|[Bottom caption]}}
See also template:Double image for horizontally stacked images and Template:Multiple image.
Examples
To the left, with one single caption:
{{Double image stack|left|PNG ... 1.png|PNG ... 2.png|200|A PNG image...}}
To the right. With two captions, one beneath each image:
{{Double image stack|right|PNG ... 1.png|PNG ... 2.png|200|A PNG image...|...here overlaid...}}
A PNG image with an 8-bit transparency layer (top), overlaid onto a checkered background (bottom).
A PNG image with an 8-bit transparency layer...
...here overlaid onto a checkered background.