Digital cameras are a great aid for the painter. I'm showing a way of using a digital camera to help paint a watercolour of a complex subject. The subject is the Trevi Fountain in Rome which gets so crowded I would find it impossible to paint on the spot. I had to resort to taking lots of photographs.
The first stage is to crop the photograph to find a good composition. I did this in Corel Photopaint an alternative to Photoshop. These programs also let you superimpose a grid. This is useful when you have a complicated subject. Here's a screen grab of the active Photopaint window
I set the grid size to one quarter of the width of the paper I was using. It's easy then to feintly draw the grid on the paper and make a careful outline drawing. Using a grid to transfer an image to paper or canvas is a well established method.
I painted the watercolour with the image displayed on a laptop. It's obviously not a straight copy. I've left out much of the background detail so that the focus of interest is the falling water. This was painted by first using masking fluid and later using 'drybrush' (ie with little paint on the brush and dragging it sideways rather than using the point.) This way you can exploit the grain of the paper to achieve a nice broken texture.I used a heavy Waterford rough.