Nicola Kirkbride's photo appeared in hundreds of stores across the country after it was taken from her university blog and put on the front of a girls' top.
She found out about it only when a worker at the supermarket contacted her on Twitter to say she had seen her image on the sweater.
Stunned Nicola, 22, said: "I couldn't believe it. I went to Tesco and there it was hanging on the rail. I bought it for