(if this is not what u have asked comment ur question again)
okay what i understand is.
1) to create a random name you can use
time() in name of file because random function has the probability that two files names could be same (if that could be a problem with your system). e.g.
time().$_FILES["uploadPic"]["name"] // if file name is john.jpg
it will save file name something like 1302827272john.jpg
2) i am not clear what u have asked... but this might help..
it would be better if u use multiple columns for picturePaths for one record
but if you have only one column of picturePath then you can update the previous field by apending new file name with old file name.. for example
// get old path using
Select picturePath as path
where your_table.id = '1';
$path = path.','.$newFileName; // this is suedo code
// update your picture path using update query
update table_name SET picturePath = $path where id = '1'
and remember now you have to split picture paths when u will use it you can use
preg_split('/,/', $path, -1, PREG_SPLIT_NO_EMPTY);