Place your coaster over the part of the comic that you'd like as the image for your coaster and trace around it.
cut out what you've traced
on plain white paper, trace around the images you've just cut out and stick the white pieces to the backs of the comic images you're going to use for the coasters.
use spray glue to stick the images to the coasters.
allow to dry.
coat the images(now stuck to the coasters) with modge podge and allow to dry.apply a second coat,painting inthe opposite direction to the first coat(eg.if you painted the first coat from right to left,paint the second coat from top to bottom)
allow to dry between coats
paint modge podge on the glass and 'stick' it onto the front of your coaster. apply pressure. allow to dry. done :)