When I started my blog, I used Picasa to upload the occasional photos. I suppose blogspot had a photo upload system, but it wasn't obvious to me. Later I picked it up and did not bother with Picasa anymore and instead like so many do, I used Flickr. But Flickr is limited if you don't pay for it. Now I learn that Picasa has all my pictures archived and I can embed a slide show. Of course learning it and actually being able to do it, are two separate matters.
The above was written a week or so ago. I set up Picasa and embedded the slide show into my blog and I have taken a second look at it to see if I can alter it, but it would seem not. The problem is that it starts showing the same photo each time and goes in the same order each time. So I, and anyone looking, only sees the same photos.
I have just uploaded two hundred of my latest blog photos to Flickr and I will put the Flickr slide show back soon. Flickr will only show the latest 200 photos, but at least at random.