There is nothing wrong in using photographs you stumbled in the World Wide Web in your posts. Of course, there will always be photos out there far more interesting, creative and beautiful than your own photos. There is no harm in utilizing them provided you follow protocols and proper etiquette, which basically covers the following points:
• In using photos other than yours, in your blog posts or other functions, do not claim others’ work as your own and always make sure to give credit where credit is due. Acknowledge the owner of the photo by providing his site (for example, 5th wheel insurance) or url in your blog post
• Being that it is an intellectual property, always check whether the owner actually allows people to use his works, because it is a crime to do so if it stated otherwise.