Today, I'm gonna show you how you can link your (or anyone else's) Flickr account to Blogger slideshow gadget. And as a bonus, I'll show you how you can particularly link a single set (playlist, category) from your Flickr account to play as a slideshow in your Blogger slideshow gadget.
It should be obvious by now that you do not need flickr account's password to play the images in your slideshow. As such, you could easily play someone else's images in your slideshow. For example, if you use my profile name as shown in the example above, you'll be playing my images. I strongly suggest you ask for the permission from the owner of the images that you're going to be playing in your slideshow before adding them to your blog.
And BTW, do watch Transformers Dark of the Moon. The coolest movie ever! If you don't like it, you must hate fun.