But the important thing is: Do *NOT* give a value for an AUTO_INCREMENT field (other than NULL) unless you have a really damned good reason for doing so.
If, for example, you were to do
INSERT INTO product_images( imgID, productid, imgName ) VALUES( 77316, 1, 'bench1.jpg' )
INSERT INTO product_images( imgID, productid, imgName ) VALUES( NULL, 1, 'bench2.jpg' )
then the record for "bench2.jpg" would have an imgID of 77317.
The principle: If you don't give a value to the auto_increment column, mySQL always assigns a value one more than the current maximum value in the column.