Passing Pinterest nopin code?

You can completely customise the output of the widget. From the FAQ:

In version 1.4 and above you can also customise the image loop completely by creating a parts/wp-instagram-widget.php file in your theme.

In version 1.9.6 you can now use a filter to change the location of your custom template part: wpiw_template_part.

Creating this custom template part allows you to create custom HTML for each image. The relevant code is here: https://github.com/scottsweb/wp-instagram-widget/blob/master/wp-instagram-widget.php#L104-L109