The other posters are correct that if you only have a very occasional need to create edible images, it probably makes more sense to have someone print them for you (if you can convince them to).
If you decide it is something you want to do regularly, then you can purchase a turnkey system which will range in price from $350-$4,500 depending on the bells & whistles. The major distinction with a turnkey system is that you will usually (not always!) receive a custom decorating software package which will greatly simplify the printing process and also allow you to easily print edible images for cookies and cupcakes, as well as cakes.
Another option is to just buy a suitable printer (usually a Canon inkjet) and then buy edible ink cartridges and edible icing sheets to use for edible printing with the inkjet printer. It is critical that you use a brand-new printer, and NEVER use regular ink cartridges in the printer if you will be using it for edible printing. The key issue when choosing a printer is whether edible ink cartridges are available for it. Of course, you will also need a suitable software package to make it all work properly.
In the interest of full disclosure, we are a distributor of the supplies and printing equipment, but to be fair in this forum, in addition to us, there are several companies, including Photofrost and Kopykake, that supply the types of items that may help you.
If you have questions, feel free to ask. We will be happy to explain the options and let you know if we can help, or if another company has a better solution for your particular situation.
This can be a very interesting endeavor, and with some initiative, can become quite a business opportunity. The key is marketing your product, because there is definitely a demand out there for picture and logo cakes, cookies and cupcakes. Think car dealers, real estate agents, banks, hospitals, ad agencies, corporations--just about any business that needs to market themselves.
Sweet Art Company