In general, we rely on two main websites to do our post processing, PicMonkey and BeFunky. They are both free, but they both have special extra features for those who subscribe at a rate of about $30 per year. If you make many posters, greeting cards, or FB special posts, you may find the subscription worth it. Both programs are user-friendly and easy to learn. We also have Photoshop Elements, but it is not as intuitive and so more time-consuming.
Both programs have a sketch option, and there are also sketch apps available for smart phones as well.
The following are just experimenting to the point that we don’t remember all the things we did to them. The upper left is of reflections in a puddle in the Sam’s parking lot; the lower left is from the Hispanic Cultural Center; and the eagle is a carving from the Montano Sculpture Garden.
The two photos below are from “Posterize” on PicMonkey, called “Cartoonizer” on BeFunky.