First of all thanks for the great plugin, it truly is an outstanding work and all the 5 star ratings including mine speak the same. However, inserting your credit link without prior permission of the users are against WordPress Policy and I'm sure most don't appreciate the fact.
"The plugin must not embed external links on the public site (like a "powered by" link) without explicitly asking the user's permission." - WordPress
Please consider giving the option to your users to show or not show the link.
Correct me if I'm wrong but I don't see anywhere in the settings that this can be turned off.
Here's what shows up in the pages source:
<div class="slideshow_plugin_manufacturer"> <a href="http://www.stefanboonstra.com/slideshow/">WordPress Slideshow</a> </div>