Specify the URL of the image to be used as a watermark, which can be added to the Z image.
You can use image API parameters for the specified image URL.
Example) ?mark=https://example.com/watermark.png

You can specify the transparency of the watermark.
Example) ?mark-alpha=60&mark=https://example.com/watermark.png

You can specify the placement of the watermark. The default is set to bottom and right.
Example) ?mark-align=top,left&mark=https://example.com/watermark.png
