Manipulating Blob Fields

Hi, this is my first posting to this group, so I hope it gets to the right place! I have been experimenting with uploading image files and storing them in a mySQL database table. So far I have been able to upload and extract data from an image file, add it to the database and subsequently display it. I can also resize, etc. so long as I have the original file to process. What I cannot fathom is how to do this by reading image data stored in a blob field in the table rather than a file. Most of the image functions seem to need a file as the source. Anyone help a newbie? Alan Bannister