Image classification using Neural Net Pattern Recognition app

I have 240 black & white hand posture images which I need to classify into 10 classes. I planned to use the Neural Net Pattern Recognition app to classify the images. I have arranged the images into a 1x240 cell array to set as input, for output I arranged an image from each classes into 1x10 cell array. The image sizes are all same. My problem is the output array does not appear as a choice in the app when I want to choose the target output. Is there any data configuration or rules when it comes to input and target data? Or does anyone has an example on this? Your help is truly appreciated!