Hi I am building a programming training course, where there are several projects I will be adding to my course, for students to get an understanding of  the building process.
 
My question is that the images I use in my projects, are there any rules around the images, do I need to buy copyright shutterstock type images?, or I can do an image search on google and just use those thimbnails inside my sample projects. 
 
Thanks in advance.
 
Fahd