How Sirius recognized Pettigrew / Scabbers

'Then it's time we offered you some proof,' said Black. 'You, boy - give me Peter. Now.'
'Come off it. Are you trying to say you broke out of Azkaban just to get your hands on Scabbers? I mean how's he supposed to know which one he's after if he was locked up in Azkaban?'
'You know, Sirius, that's a fair question. How did you find out where he was?'
Black put one of his claw-like hands inside his robes and took out a crumpled piee of paper, which he smoothed flat, and held out to show the others.
It was the photograph of Ron and his family that had appeared in the Daily Prophet the previous summer, and there, on Ron's shoulder, was Scabbers.
'How did you get this?' Lupin asked Black, thunderstruck.
'Fudge. When he came to inspect Azkaban last year, he gave me his paper. And there was Peter, on the front page... on this boy's shoulder... I knew him at once... how many times had I seen him transform? And the caption said the boy would be going back to Hogwarts.. to where Harry was...'
'My God... His front paw...'
'What about it?'
'He's got a toe missing'
'Of course,' Lupin breathed, 'so simple... so brilliant... He cut it off himself?'
'Just before he transformed. When I cornered him, he yelled for the whole street to hear that I'd betrayed Lily and James. Then, before I could curse him, he blew apart the street with the wand behind his back, killed everyone within twenty feet of himself - and sped down into the sewer with the other rats...'

THE SERVANT OF LORD VOLDEMORT - Pg 385