Storing user-uploaded files on a webserver

What Matt H suggested is a good idea if what you are trying to achieve is per user level image access. But granted that you are limited in your database stored space, storing the images at binary data is inefficient as you stated.

Using a table per user is bad design. The user who uploaded the file should simply be a field/column in the table that stores all file uploads, along with any file metadata. I suggest generating a GUID for the file name, which is guaranteed to be unique, and better than an autoincrement field which is easy to guess if you are attempting to prevent users from simply accessing all the images.

You are concerned about performance, but until you are dealing with millions upon millions of records, your queries for selecting images belong to a user, uploaded within a specific time frame (say you are storing a timestamp or similar) are minuscule in cost. If speed is an issue, you can add a B-tree index on the username, which would speed up your user specific image queries significantly.

Back on the topic of security, access and organization. Store the images with a folder per user (although depending on the number of users, the number of folders may grow to an unmanageable level). If you don't want the images to be publicly available, store them in a non-web folder, have your application read the data and stream it to render the image for the user. More complex but you hide the actual file from the internet. In addition, you would be able to validate all requests for an image by an authenticated user.

It depends on the nature and structure of your app and database. I've used many techniques, including folder-based, pictures stored in a database blob, off-web file folders accessed through an authentication gateway...

For external images that aren't directly related to the app or database, like temp photos or something, I tend to put those in a folder. Since it seems like your structure is pictures from a user, then I would expect there might be metadata associated with the image, such as tags. In that case, I would probably store the picture in a database table, assuming I had the capacity for that. If the photos needed to be secured, inaccessible to other users without authentication, then a database would have its own security, whereas a file-based storage would need some sort of trick to prevent unauthorized access.

I wouldn't use a table per user, just a table of Pictures with elements of ID, userid, picture blob.

Does that help?