Thanks everyone for the input and suggestions.
The environment I am working with is accredited (read "takes and act of god to add/remove software requirements such as SQL, Postgres", etc) and hardened. Additionally it is hosted on one of our customer's systems. So short answer concerning environment, I have very little control. The images that are being sent are being sent to this one vendor from multiple hands, all with a defined file format, so unless I decide to rename everything I need to store additional info. I should also mention I plan to write a web app to run reports on submitted/non-submitted/incomplete collections. Using memory might be an option, though I do not know how long I need to make sure this information is available. I do know that 10s of thousands come in daily, so I guess I will have to weigh in on File IO choking vs hogging resources.