File Upload: Temporary File Location

What I'd like to do: I'd like to upload images into the mysql db via the browser's upload functionality (POST). Now I encountered the following problem: During the uploading process php or the webserver (I'm not sure which) creates a temporary file in a tmp directory, whose path I can find out by looking at the phpinfo(): upload_tmp_dir, TMP or TEMP. (How do I set them). Acutally none of them is set. What's the defalut path? In this directory the webserver has actually (because of security reasons) no write privileges. So it cannot create the temp file, which leads to having no file neither to copy somewhere nor to insert into the db nor to unlink after all. What could I do without giving full write access to the webserver? My proposal: create a separate php/webserver tmp dir with with read&write, but without executable privileges. I know, that with phpinfo() I can find out where php tries to save tmp upload files. Thanx for tips&tricks Steff