Dots Per Inch
dpi
Sets the DPI value in the Exif header of JPEG files. It does not alter the web display of the image.
The DPI value affects the print size of an image. For instance, an 1800×1200-pixel image set to 300 DPI will print at a size of 6”×4”.
This parameter only works on JPEG and PNG files. To apply DPI to other file types, combine the dpi parameter with the format parameter (either fm=jpg or fm=png) to convert the file to a format that supports the DPI Exif header.