|ICEFIELDS by Sea Dean painted from an image by Petrina McNeill|
Available as an Art card, Postcard and Mini Magnet here
I occasionally copy free online images for my art, but generally I use them only for inspiration or I collage together many separate bits (adding a deer to a tree and a mountain for instance) and then paint the new composition. Trying to copy a photo exactly never works anyway, because the two media use different compositional rules and the lens sees light differently, so it is important to use your artist training to adapt the photo into a painting.
That having been said, if you're stuck for subject matter, or searching for a different viewpoint, there is no harm in browsing free photo sites. Here is a link to the most popular sites. On some websites, if you are going to sell the finished work and if the image isn't altered enough, you must be careful to read the license agreement because commercial use may be restricted, or you may need to give recognition to the photographer.
FREE IMAGE WEBSITES
I haven't used all of these but you will eventually find your favourites. Personally, I've used Morguefile and then went on to Paint my Photo, but now I use Pixaby. If I'm only looking for inspiration, I find spending a fun hour with Pinterest usually works and it is very relaxing which is always a good thing.