Is this art or rubbish?

When park workers removed this graffiti-covered discarded mattress, they had no idea they were dismantling a piece of modern art worth £1,000. The apparent rubbish was a work by Johnny Doe as part of the Art Free For All exhibition in Alexandra Park, north London. One of the organisers realised the workers' mistake in time and stopped them before they reached the tip.
The exhibition features works by 35 artists dotted around the park. Telegraph photographer Eddie Mulholland wandered around Alexandra Park taking pictures of objects that caught his eye. The question is: are they art or rubbish?