As a teenager in the 1960s, he was told there was no such thing as a Black photographer. Today, the work of Dennis Morris includes some of the most iconic music portraits of our time. Official photographer for the likes of Bob Marley and the Sex Pistols, his images defined music history. Now, his full collection is on display in the "Music + Life" exhibition at the MEP photography space in Paris. Dennis speaks to Culture Editor Eve Jackson about how it all began – as a teenager bunking off school to meet his hero.