Whenever autograph collectors are searching the Web for new treasures, I always recommend they take the time to check the signatures they desire against as many valid examples as possible to really build their knowledge, and confidence, when collecting signed photos of any celebrity.
I suggest you open a new window or two and use sites like:
R & R Auctions, Rolf Ramseier, Is It Real, History for Sale & Autograph World, Autographs 101
to check signatures regularly so that you familiarise yourself with the signers style and expected price range to avoid making unnecessary mistakes. These dealers offer templars of in person signings so that you can make comparisons and also note variations. Some signers change styles very little over the years and some merely squiggle whatever style takes their fancy at the time. Some will even sign entirely differently if they don't like the person chasing their autograph. So it is important to know what to look for when collecting a certain celebrity.
Even the most experienced dealers have their war stories about mistakes they've made. Only constant checking and cross- referencing leads to minimising costly mistakes. This is a great hobby, but it is also a business prone to forgers and unscrupulous sellers on various sites across the globe. There are also numerous actors/models who use autopens, secretarials, or rely on inferior laser and inkjet prints that are often well worth avoiding. Preprints are also a problem on the Net when sellers try to sell them as authentic items. Many of these are also copies of forgeries mainly because the photo content is sexier than the actual autograph.