Not quite ready to tackle a slideshow, I started with a mosaic image, using Image Mosaic Generator. Their advice is to stand back from the image about 5 meters to see it at its best. I settled for shrinking it to about 20% of original size. So see Multnomah Falls as made up of dillions of other people's images:
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By the way, many of the photos that comprise those yellowish trees on the left are of rubber duckies:
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Now ready to put together a slideshow, I started out by trying Animoto through Facebook. I quit after seeing that even though they had 146 reviews, they weren't scoring very high--and it looked like they'd made the reviews disappear. After that, I figured I'd just go for a no frills Flickr slideshow.
Okay, it's not playing music, but I can live with that. Pop music didn't seem to go with all those nature photos anyway.
I wouldn't say the services I tried worked "smoothly." Flickr, which you'd think would be solid and established by now, locked up when I tried to sign in. Animoto was behaving less than trustworthily. Yet I remember ten or fifteen years ago when creating a music video of your photos or video clips was a massive undertaking, done only by the truly dedicated, and now it's a free service that basically just asks for you to do some uploading. I might play around with this more when (if) I have more free time. We did a Flickr tour for our library. I doubt music and fancy transitions would improve it any, but we can always keep the possibility in mind.