The 2 answers already covered it pretty well. It is indeed best practice to save the directory path instead of saving the entire URL path. Some of the reasons were already covered, such as making it easy to move your folders to another server without having to make any changes whatsoever in your file logic.
What you could do, is also have everything in one directory, refer to that, and then just save the image name. However, I would not recommend that. The other structure simply makes it way easier to navigate and look through. Good file structure is something you'll thank yourself for later in case you ever have to go through things manually for one reason or another.
With that said, I'd like to add this trick into the mix:
$_SERVER['DOCUMENT_ROOT']
. This always makes you start from the root directory as opposed to having to do tedious things, such as ../../
etc. It looks like a mess.
So in the end as an image path, you'd have something like:
<img src="<?php echo $_SERVER['DOCUMENT_ROOT'].'/'.$row['filePath']; ?>" >
$row['filePath']
being your stored filepath from the database.
Depending on how your file path is saved, you can lose the /
in the image source link.