http://www.ehow.com/how_5384347_make-custom-tattoo-online.html

Creating a custom tattoo online is a great way to design a tattoo that can have all of the elements you want, because you created it. There are websites that allow you to create your own tattoo online by uploading an image, drawing your own tattoo, or tweaking an existing idea from their gallery of pictures.
Instructions

Things You'll Need:
Active internet connection
Custom Tattoo Design
Step
1

Research the type of tattoo you want. Think about what you want the tattoo to represent. Are you getting the tattoo in honor of someone special, to commemorate an event, or just as a form of expression? Search online or look in magazines for a picture that inspires you. You don't just have to look at pictures of existing tattoos. If you find a picture online that you like, save it to your computer in .jpg format.
Step
2

Visit a website that allows you to upload custom tattoo designs. StrayTats.com has three ways for you to create your own custom tattoos. You can upload a digital picture from your computer, draw your own tattoo using their beta application or choose a tattoo from their gallery.
Step
3

Customize the image after you've uploaded, chosen, or created your tattoo by adding text, changing colors, or cropping your photo. When you are finished editing, click "File," then "Save" to save the image to your computer. The file will save in .png format.
Step
4

Finalize the tattoo details by selecting the size of the tattoo you want using the slider at the bottom of the screen. Then, select the number of copies you want to purchase.
Step
5

Click the "Update Order" button under the size slider at the bottom of the screen. Review your order and shipping costs, check the ""I agree to the terms of service" box, then click the yellow "Checkout" button and enter your payment details. You should receive your tattoo in 3 to 5 days.