I recently completed a similar task for a client. I had to implement the entire signature pad though, from start to finish. In my experience, saving directly as an image is not as secure or convenient, and will obviously take up more space and resources. After several methods was tested to see which would truly suit the requirements best, I decided to go with an implementation that saves a PNg signature instead of a direct image. The PNG signature is posted to the database instead of the filename, and then whenever the signature needs to be displayed on a browser or perhaps a pdf document (both requirements from precious client) a simple decode string in php allows for the signature to be displayed as an image. I highly recommend a similar approach to your task, but this is just a suggestion from my side based on previous experience.