Before reading this article, it would be a very good idea to get a book on photo offset printing, for this is the method used in counterfeiting US currency. If you are familiar with this method of printing, counterfeiting should be a simple task for you.
Genuine currency is made by a process called "gravure", which involves etching a metal block. Since etching a metal block is impossible to do by hand, photo offset printing comes into the process.
Photo offset printing starts by making negatives of the currency with a camera, and putting the negatives on a piece of masking material (usually orange in color). The stripped negatives, commonly called "flats", are then exposed to a lithographic plate with an arc light plate maker.
The burned plates are then developed with the proper developing chemical. One at a time, these plates are wrapped around the plate cylinder of the press.
The press to use should be an 11 by 14 offset, such as the AB Dick 360. Make 2 negatives of the portrait side of the bill, and 1 of the back side. After developing them and letting them dry, take them to a light table. Using opaque on one of the portrait sides, touch out all the green, which is the seal and the serial numbers. The back side does not require any retouching, because it is all one color. Now, make sure all of the negatives are registered (lined up correctly) on the flats. By the way, every time you need another serial number, shoot 1 negative of the portrait side, cut out the serial number, and remove the old serial number from the flat replacing it with the new one.
Now you have all 3 flats, and each represents a different color: black, and 2 shades of green (the two shades of green are created by mixing inks). Now you are ready to burn the plates. Take a lithographic plate and etch three marks on it. These marks must be 2 and 9/16 inches apart, starting on one of the short edges. Do the same thing to 2 more plates. Then, take 1 of the flats and place it on the plate, exactly lining the short edge up with the edge of the plate. Burn it, move it up to the next mark, and cover up the exposed area you have already burned. Burn that, and do the same thing 2 more times, moving the flat up one more mark. Do the same process with the other 2 flats (each on a separate plate).
Develop all three plates. You should now have 4 images on each plate with an equal space between each bill.
The paper you will need will not match exactly, but it will do for most situations. The paper to use should have a 25% rag content. By the way, Disaperf computer paper (invisible perforation) does the job well. Take the paper and load it into the press. Be sure to set the air, buckle, and paper thickness right. Start with the black plate (the plate without the serial numbers). Wrap it around the cylinder and load black ink in. Make sure you run more than you need because there will be a lot of rejects. Then, while that is printing, mix the inks for the serial numbers and the back side. You will need to add some white and maybe yellow to the serial number ink. You also need to add black to the back side. Experiment until you get it right. Now, clean the press and print the other side. You will now have a bill with no green seal or serial numbers. Print a few with one serial number, make another and repeat. Keep doing this until you have as many different numbers as you want. Then cut the bills to the exact size with a paper cutter. You should have printed a large amount of money by now, but there is still one problem; the paper is pure white. To dye it, mix the following in a pan: 2 cups of hot water, 4 tea bags, and about 16 to 20 drops of green food coloring (experiment with this). Dip one of the bills in and compare it to a genuine US bill. Make the necessary adjustments, and dye all the bills. Also, it is a good idea to make them look used. For example, wrinkle them, rub coffee grinds on them, etc.
As before mentioned, unless you are familiar with photo offset printing, most of the information in this article will be fairly hard to understand. Along with getting a book on photo offset printing, try to see the movie "To Live and Die in LA". It is about a counterfeiter, and the producer does a pretty good job of showing how to counterfeit. A good book on the subject is "The Poor Man's James Bond".
If all of this seems too complicated to you, there is one other method available for counterfeiting: The Canon color laser copier. The Canon can replicate ANYTHING in vibrant color, including US currency. But, once again, the main problem in counterfeiting is the paper used. So, experiment, and good luck!