Sets the image_size property to image_size.
Valid sizes are described in the <ulink type="http" url="http://code.google.com/apis/picasaweb/docs/2.0/reference.html#Parameters" >online documentation</ulink>.
Set image_size to null to unset the property.
| this | |
| image_size |
the desired size of the image to be retrieved, or null |