Minimum Printed Watermarked Image Size: 2″ x 2″
You can go smaller if you increase the watermark strength, but below 1″x1″ scan success becomes highly dependent on the quality of the phone camera, which is unpredictable.
Maximum Printed Watermark Size: 5.5 feet x 5.5 feet
This is based upon the following assumptions: Maximum allowed pixels in an image that can be watermarked is 100,000,000. If we assume a square image, that is 10,000×10,000 pixels per side. Minimum recommended print resolution is 150 DPI (dots per inch, or pixels per inch, if you want to think of it that way). So [10,000 pixels] divided by [150 pixels per inch] divided by [12 inches per foot] = 5.5 feet per side.