You can make an edible image icing plaque like this:
http://cakecentral.com/article163-How-To-Make-an-Edible-Image-Icing-Plaque.html
If you don't have a printer, you could take them to a bakery and have them make the images.
Or, you can make them the way that I have been making my plaques. You can see an example of them in my photos. The Harley vest and cap and the Sesame Street cake here:
http://www.cakecentral.com/cake-decorating-gallery_display_687233.html
Here's how I made them.
1. Print out the design to be copied on regular paper. (You can scan or copy some playing cards or seach for photos already on the net)
2. Put the paper in a sheet protector.
3. Very lightly grease the plastic protector.
4. Roll out straight gumpaste on sheet protector so that it is thin enough for you to see the design or image through.
5. Cut out design with an exacto knife
6. Trace over the design with edible markers.
7. Fill in design with markers or edible paint (icing colors thinned with alcohol).
8. Let dry and remove.
9. Place on cake.
If you have to roll the gumpaste really thin in order to see small details, the plaques will be very thin and break easily. To make them thicker, I have put them on another layer of gumpaste before they dry and attached them with some gum glue or vanilla. That way, they are very sturdy.
I hope that makes sense.
Renae
The ones I made on my "Vegas" cake (in my photos) were very easy. I just rolled out white fondant and cut out several 'cards' of the same size - I just kinda eyeballed them to make them look proportionate. I dried them overnite. Then I used the Wilton Foodwriter Edible Color Markers to make the cards. I just kinda free-handed them.
HTH
LadyMike
wow infields, what a great idea! i've been trying to figure out how to do this without a printer.....usually, i can free hand most stuff......but there's some pics that i just wish i could trace! u've got it all figured out! 
What about chocolate transfers? You would need to have the cards printed out in reverse though to start. http://www.geocities.com/heathers_cakes2000/chocolatedemo.html?1109787013625
a bit more expensive, but I always send away for my images because so many of the bakeries are inconsistent with lightness, darkness, and inexperienced help. I go to icingimages.com and send them an image from google images. When the image comes back, I use royal to glue it to gumpaste. Then cut around the edges and let it dry. I love their customer service. You can put more than one image on a page and cut the cost. They make it whatever size you want. Very professional
http://www.unforgettableweddingcakes.com/more%20ideas/grooms/Page%201/html/bulldog%20flush.htm
I haven't tried it, but I bet rice paper would work great! You can see through it, so you could put it on top of the card and use markers (Wilton foodwriters, or similar) or icing colour thinned with vodka/vanilla and simply trace then color in the design. Jackie has instructions posted on how to make realistic butterflies this way. You could always put the "card" on white fondant cut to the same size, to get the white background (or just lie it on top of white BC). Good luck! Now I want to try making a cake with playing cards.... 
Here is a recent cake I did. I made the cards using white chocolate bark spread on 2 in x 4 in pieces of acetate and when hard peeled off the acetate and used piping gel to glue the edible images on. I can print 6 cards per 7.5 x 10 frosting sheet. Everyone thought they were real playing cards. If you need someone to print them for you just PM me and we can talk about it.
I used color flow to make mines. Takes more time than what everyone else suggested but didn't know any better. I then placed the actual design on a piece of dried gumpaste (with royal icing) in the shape of the card. This was a very large playing card though so I wouldn't suggest my way for multiple cards 
Quote by @%username% on %date%
%body%