Function only for widgets (lightbox data attribute)

Hi there guys,

I wonder if there is a way to add function only to widgets.

I was planning using blueimp lightbox for my images, but since it includes all images from the page into the same lightbox I wanted to split images from widgets and images from page/post

I used this code

function add_rel_to_gallery($link) {
return str_replace('<a href=', '<a data-gallery="#blueimp-gallery-test" href=', $link);
}
add_filter( 'wp_get_attachment_link', 'add_rel_to_gallery' );

to add the data attribute to media links, well that works, but can you add this function only to widget areas or only to posts and pages?