We all know it's really important to offer credit where credit is due. In speaking at a lot of conferences, I also end up watching a lot of speakers give talks and I've seen quite a few ways folks include credits. Some do a bibliography slide (or two) at the end. Some include a link to their reference in really small text on the slide where the reference is made.
I do a bit of a mix, depending on what I'm talking about. For example, if I've used a photo from the internet, I tend to put the URL where I found the image in the slide notes, (it will show up if people download the slides, which lots of people seem to do.)
In the case of referencing a book, or a quote or story I'm referencing from a book, I tend to show the whole book cover - if I'm really on my game I'll include a link to the book on Amazon in the slide notes.
However it gets done, it's an important thing to do.
Don't forget to include credits and attributions in your talk!