Where are the tourists?
At this time of year, Lafayette Square is loaded with tourists, but none are in this image:

The solution is to take multiple photos, each with the tourists in slightly different places, then combine them in Photoshop. Photoshop offers an automated way to do this – using “image stack”, designed for scientific purposes but working well to combine photos based on several different algorithms.
I got pretty close to the no-tourist result this way, with a few ghost areas left behind. So I refined the results manually – stacking the photos and masking out certain areas from each layer.
What would have been better for next time:

1. take more photos – I only took 6 images, and while there weren’t people standing in the same spot in each image, there were a couple of spots where one person would be there in one image and another person in the other images.
2. use a tripod. I took these shots by sitting my camera on a bench and using a cable release, but even so, when I used Photoshop to auto-align the images, it was clear that there had been camera movement between the images.