A while ago, I picked up a 'cheap' 2GB SanDisk Ultra II SD card for my (then) shiny new Canon IXUS 80is on eBay. The price was a bargain, the seller had good feedback, and the photos of the product showed that the item was brand new and boxed. So, I had no hesitations in buying the card.

Last week, the card failed on me. I took a bunch of photos of Aimee on it, ejected the card from the camera and popped it into my desktop. Debian etch's Gnome usually automounts SD and USB media, so I was surprised when it didn't automagically appear on my desktop.

I had a load of error messages in dmesg, saying that the kernel hadn't been able to find a valid filesystem on the device, and the ominous DriveReadySeekComplete messages confirmed to me that the card was toast.

Annoyed, but unconcerned, I pointed Firefox at www.sandisk.com and set about claiming on SanDisk's generous 10 year warranty. I emailed them with details of the card, like the serial number on the back, and a brief summary of what's wrong with the card - asking for advice as to how I'd have the card replaced. To my utter disappointment, I received a reply telling me that the number given was invalid, and that it was highly likely that I had purchased a counterfeit card.

In the mean-time, I'd ordered a replacement card from MyMemory.co.uk - £15.99 for the same card was excellent value.

This card arrived today, and with both cards in hand, I can show you the differences between the two.

In the following photographs, the fake is on the left and the genuine card is on the right.

At first glance, the cards look identical. It's only when you take a close look that you can spot the differences.

1. The rim at the bottom of the card. On the genuine card, this has a small indentation. On the fake, it is solid.

2. The sticker on the card. The fake uses a shiny, silvery print as the backprint of the entire sticker. So the words SanDisk, Ultra, Lock, 2.0GB and the bottom SanDisk logo all have a 'shiny' appearance. On the genuine card, only the 'Ultra' branding is like this. The SanDisk logo at the bottom is printed in white, and the top SD logo has a non-shiny golden background.

3. On the rear. The first thing you should notice with a geniune card is that the capacity is printed on the rear, and there is an embossed SanDisk logo engraved into the plastic. The fake card does not have any of these markings. There will also be a serial number. My particular card is MADE IN CHINA, and the fake is MADE IN TAIWAN.

4. It's worth noting that my fake card came retail boxed, and really did look the part. It came in a cardboard outer, with a plastic card case, and paperwork and documentation claiming to be from SanDisk. The real card came in a (really, really, really difficult to open) heat-sealed plastic pack.

My only advice - don't buy flash memory off eBay. I hope this little guide helps.