The signature was real, but the picture provided to Shoaib was of some other woman.
Its Shoaib's word against hers, unless she emailed the picture and there is some track that still exists on hotmal/gmail. However Rashid Latif has come forward and said that since Shoaib being a metric pass lallu, always came to him to chat with Ayesha and used his laptop and the pictures he saw of Ayesha were of a different one than the big girl we see on TV these days. So Shoaib has a witness.
Shoaib's other line of argument would be that the nikah procedures used were wrong, since according to Pakistani law, telephone nikah is no longer considered jaiz. Nikah performing Maulvi has to physically SEE the man and the woman and then proclaim to each other the names of them and take it upon himself that the people they claim they are, are the people he is actually marrying. So even though he had intent of marrying a woman, the woman cannot be verified as her even by the maulvi and ultimately the nikah is false.
There are a bunch of screwed up Indian laws in the middle as well which will play against Shoaib. Basically an passingby woman that has a photo of you and her together, a few witnesses to go along can claim that you two got married.