Instructions
Look at the front of your R4i card for the white circle with the 'i' in it. If your R4i card is authentic, the 'i' will fit in the circle with plenty of white around it. Fake R4i cards have a bold 'i' which practically touches the top and the bottom of the white circle.
Study the circuit board on the back of the R4i card. Authentic R4i's will have 'r4i' printed in white in the top left corner of the board. Also observe the gold strips. They should all be longer than those on a fake card and will practically all reach the bottom of the board.
Look at the box and the cartridge itself. Official R4i cards will have the correct website listed as www.r4i-sdhc.com. If your R4i card has any other web address on it, then it is a fake.
Turn the R4i card around to the back. Authentic R4i cards will feature a holographic sticker which states "Please Access the Official Web Site TRUTH ENQUIRY" which you can peel off to reveal a four-tiered code. Visit the website printed on the front of the R4i card and click the "Forgery-proof search" link in the top right corner of the screen. Enter the number into the box provided for confirmation of authenticity.