PicApp is an online service that provide quality images for free use to bloggers and other online publications without having to think about copyright or legal issues. You can simply enter search terms and obtain the desired images to be published, choose the image size you want, and grab the code for publish.
The best thing about this service is that we can use desired image for publish without the fear of copyright or legal issues. However PicApps includes some advertisement over the image and also some sponsored links.[source]