For images, we strongly recommend to use the cook uploader instead of Joomla! native image picker and media manager. Few reasons:

• The native Joomla! image picker cannot work on 2 different fields in the same page.
• Files are not stored in hidden path
• If you plan to move / migrate your application, you gonna need to be very carefull to preserve the images paths correct.

With indirect access, you will be able to move the media folders easily, because the database only stores short relatives paths.

In the builder, in the field properties, you can set up the upload options.

Renaming rules

This is the most important about files...

The file is always renamed before to be stored.

Using tags:

• {BASE} : Original file name without extension.
• {ALIAS} : Safe aliased base name.
• {EXT} : Original extension.
• {MIMEXT} : Extension from Mime-header.
• {ID} : Id of the row item
• {RAND} : Randomized value
• {DATE(Y-m-d)} : Formated date.
• {...#6} : Limit to 6 chars. 
  ex : {ALIAS#6} ; {RAND#10}

You can create relative sub folders:

ex: {ID}/{RAND#8}.{MIMEXT}

You can also choose the special behaviors when a file is found with the same name :

• Ignore
• Override
• Suffix it