bbPress.org

why do you need a plugin ?

when you reply to this comment look at the toolbar there is an image upload by url (img) button.

if you want images to be uploaded to your server

add this function to your functions php (if you have a child theme already set)

add_filter( 'bbp_after_get_the_content_parse_args', 'bavotasan_bbpress_upload_media' );
/**
 * Allow upload media in bbPress
 *
 * This function is attached to the 'bbp_after_get_the_content_parse_args' filter hook.
 */
function bavotasan_bbpress_upload_media( $args ) {
	$args['media_buttons'] = true;

	return $args;
}

but function only allows admins, moderators , and authors to upload images to your server.

you would then need to change some user role capabilities so that if you want subscribers to upload images to your server