Some posts ago we talked about great projects from museums and libraries for the digitization and the free availabillity of their collections. So in their website you can find pictures of greatest masterpieces of art, freely to be downloaded and used as the copyright holder ask.
But what about simple images for presentations, posters or other kind of publication? Can you use any image found in Google as you want? Obviously not... But today I discovered some fantastic websites.
The website collects some of the pictures made by the designer Ryan Mcguire and they are all free of copyright restrictions, does it means that you can use them as you want (even for commercial purposes)! They are in high resolution and they are fantastic! Problem: pictures are not divided by topic, so you must browse them all until you can find the one you need (but they are so beautiful that it's a pleasure to browse them).
The author only ask, in a very funny way, to donate just for a cup of coffee.
Other images can be found on Unsplash. As in Gratisography all the pictures are free and in high resolution, but they are not divided by subject.
If you do not want to waste your time browsing all the images, you can take a look at Imagebase , where you can find the following subjects: people, objects, nature, slides, city, holy lands.
If you are looking for landscape pictures, probably you will love PhotoEverywhere: all the images are under CC license, free to use but attribution is required.
Enjoy the pictures and... be creative!