Hi there Sara,
Ive had a similar problem and found the best practice being to upload the image to a specific folder and to insert the url link into the database.
If you are able to insert the image at the same time as you insert the user details in the record then you can follow many avaliable tutorials on online. If you need to update the image to an elready exisitng user record, then you would need to modify tutorials (as they for inserting new record not updating exisitng record).
Thanks