Uploaded images in MySQL

Hi to everybody... I'm working on a site in php that runs with a MySQL db... One of the table has also images stored in it as BLOBs...During the step of upload, there was no problems, but I've discovered that when I delete a record, the BLOB relative to it is non undeleted... in fact, if I add a new record, with a different image, when I show his image, I see instead the old one I deleted! I did a similar thing with postgres too... but there I knowed I had to use pg_lounlink().... I searched some similar thing for MySQL too, but I did not found anything....neither in PHP docs (even faqts), neither in MySQL docs.... Any clue? Thanks Francesco