I found this mobile phone 'pay-as-you-go' credit card on the footpath near the Euston Road bus stop. It was a T-Mobile £10 card with an image of three young people. A young girl in the centre covers the eyes of the two boys on either side of her. They are playing a game. The tone is mischievious and fun and the weather, from the light on their faces and their clothing, is hot and summery.The card looked like it had been living on the street for a while. It had a weathered patina, imprinted with footprints, dirt and gravel.

My attention was drawn to this card for two reasons and both concerned concepts of value.Firstly I have met the girl on the card. She is a model living in South Africa. She knew my flatmate and had stayed with us for a while in our London flat a few years ago.

To see her face on posters, billboards and brochures for this campaign was strange at first. But to see her face on phone credit cards which are so easily discarded and watching people walk on her image is disturbing because to me her face is more than a consumable flat image. It is a representation of a person, a personality, a collection of stories.

It made me think about other people's images which I so easily discard without a second thought to their lives. The financial transaction for a personal image is business and people entering it are not ignorant of the implications. But there is no control over where that image ends up or may be used once it enters the public domain.

The second reason the card attracted me was to do with its financial value. The card was once a highly coveted form of currency. It was purchased for £10 cash and offered £10 worth of talking. Except for its location and physical state, it still looked the same, yet its value was gone. It had been used and discarded as rubbish. It was easily replaceable.

These mobile phone cards are ubiquitous forms of currency. They can be purchased from a plethora of places - shops, supermarkets, newsagents, online and now from high street credit dispensers, similar to cash points. They offer immediate consumption without the future prospect of a bill. Like the image of the model on the cards, how the credit is used, consumed and discarded is up to the new purchaser.