How to flip an Image (Graphics or PDF) Block

In Blocks Plug-in Create an Image Block. Under Object Fitting change the scale value from 1 to

-1  1    to flip the image horizontally,
1 -1 to flip the image vertically or
-1        to flip it both ways.

Changing the scale value can also be set in optlist custom command:

Command:   optlist

Value:            scale={-1 1}

Note: Curly braces are required if two values are entered (separated by a space). For both directions scale=-1 is acceptable.

This method can be applied to Graphics and PDF blocks.