Will your images need to be named uniquely? Can the process that generates these images produce the same filename more than once? Hard to say without knowing what device is creating the filename but say that device is 'reset' and upon restart it begins naming the images as it did the last time it was 'reset' - if that is such a concern..
Also, you say that you will hit 1 million images in one month's time. How about after that? How fast will these images continue to fill the file system? Will they top off at some point and level out at about 1 million TOTAL images or will it continue to grow and grow, month after month?
I ask because you could begin designing your file system by month, then by image. I might be inclined to suggest that you store the images in such a directory structure:
where: yyyy = 4 digit year
mm = 2 digit month
D:\imgs\2010\01\aaa0001.jpg (this is why I ask about uniqueness)
Month, year, even day is good for security type images. Not sure if this is what you are doing but I did that with a home security camera that snapped a photo every 10 seconds... This way your application can drill down to specific time or even a range where you might think the image was generated. Or, instead of year, month - is there some other "meaning" that can be derived from the image file itself? Some other descriptors, other than the date example I gave?
I would not store the binary data in the DB. Never had good performance / luck with that sort of thing. Cant imagine it working well with 1 million images. I would store the filename and that is it. If they are all going to be JPG then dont even store the extension. I would create a control table that stored a pointer to the file's server, drive, path, etc. This way you can move those images to another box and still locate them. Have you a need to keyword tag your images? If so then you would want to build the appropriate tables that allow that sort of tagging.
You / others may have addressed these ideas while I was replying.. Hope this helps..