Mask 
Controls the visible and non-visible area of the image.
Mask type &mask= 
Sets the mask type from a predefined list of shapes.
More info: Issue #49 - Add circle effect to photos.
Valid shapes:
- circle
- ellipse
- triangle
- triangle-180: Triangle tilted upside down
- pentagon
- pentagon-180: Pentagon tilted upside down
- hexagon
- square: Square tilted 45 degrees
- star: 5-point star
- heart
html
<img src="//wsrv.nl/?url=wsrv.nl/lichtenstein.jpg&w=300&h=300&fit=cover&mask=circle">md
Mask trim &mtrim 
Removes the remaining whitespace from the mask.
html
<img src="//wsrv.nl/?url=wsrv.nl/lichtenstein.jpg&w=300&h=900&fit=cover&a=crop-22-0&mask=circle&mtrim">md
Mask background &mbg= 
Sets the background color of the mask. See here for the supported color formats.
html
<img src="//wsrv.nl/?url=wsrv.nl/transparency_demo.png&w=400&bg=black&mask=heart&mbg=red">md


