There are a number of web sites that offer copyright free photos that you can use as inspiration for your watercolour paintings. Some are totally free and others are free for certain uses or for certain size photos only. I suggest you read any terms and conditions on the site before you start downloading lots of images.
Copyright free photos or free for certain uses
PaintingWithWatercolors.com: This is my demonstration and reference site and contains a number of photos, usually connected to my demonstrations, that you can use as references for your own work.
PaintMyPhoto: As the name suggests this website actually encourages people to use the photos on the site as reference for your painting. It has some excellent photographic material and a friendly membership base last time I had a look.
WetCanvas.com: This group has been around for a very long time. Their library of images is quite extensive and well worth looking at if you are after some photographic inspiration.
CopyrightFreePhotos.com: Here is what they say on their site “The copyright (royalty) free photos available on this site have been made available, free of charge, for any application as you require – web design, graphics, backgrounds, printed images, desktop wallpaper & screensavers. The only exception is that images may NOT be added to other photo libraries (either online or offline) – without written permission from the site owner.”
Morguefile.com: “Free images for your inspiration, reference and use in your creative work, be it commercial or not!” Read their conditions please.
Photos4Artists.co.uk: “Photos4artists offers a wide variety of high quality, mega pixel and copyright free photos for artists of all abilities to use as reference for their art.”
If you know of any other useful sites that offer copyright free photos please let me know.