Undoubtedly on the net you can download many icons of your choice or replace them with those offered by the operating system itself (Windows), but why not create your own icons from images or photographs?
This you can do with imagicon, a free application for Windows that is simple to use, where first you will have to define the configuration of the new icon (size, color, destination) and then select the image (bmp, jpg, png) or drag it to the program so that it generates automatic icon.
Note.- By default, the program saves the icons created in the folder where the previously loaded image is located.
Official site | Download Imagicon (1.01 Mb)