how can i create trainning set for pca in matlab?

Hi all

i have a database for 49 person , 4 images/person . i need to form training set for pca by representing each image by a column contains its pixels positon .by the way my image are b/w so how can i do this in matlab ?

is the way of representing images based on their pixels locations is preferable or not? is it the only way that i can use in forming trainning set or there is another way???

thanks to all