Dynamic Images and File Permissions

I have a script that generates, creates, and updates dynamic banner images for users of a service. Recently I have run into a problem with file permissions... that has thoroughly annoyed me. I found a solution to fix the problem, however, it was then hit with another problem, and I'm not sure how secure I find my solution to be. During the image creation process, the files are given the normal image permission of 644 (rw-r--r--). Of course, this makes updating impossible. I attempted to use a simple chmod();, however, the script didnt have the permissions to do this. I couldnt figure out a way to fix this, so I moved on to looking for other solutions. I ended up with somethign that worked, slightly, but did not provide me with an actual fix due to another problem. I would connect to the folder via local FTP, then using ftp_site run a direct CHMOD on the files. However, in doing this, I feel that the script itself is insecure. Also, it didnt work in the end. After running the update script, to test out my new solution, I was confronted with a new problem that I didnt understand. The FTP command returned "Bad File Descriptor" after executing the CHMOD. After attempting in a few other of my own FTP clients, I ran into -exactly- the same problem. My questions are this: A) Is there any way to set the permissions on the file on creation of the image? B) If no, is there a way I can do the CHMOD, even though chmod(); returned insufficient permissions to do so? C) If no, is there a way I can fix the bad file descriptor, to fix the ftp solution I have? Any other solutions would be able as well, given that they're somewhat secure.