Canva is a design tool that helps you create for images Web or print, including blog graphics, presentations, Facebook covers, flyers, posters, and more.
Check out the video below to see more about Canva
Find your images: You should use copyright-free images on your posters. Since these posters be may published online you should not use other people's images that you find online unless the creators of those images have chosen a copyright that allows sharing (i.e., creative commons license). Good places to look for copyright-free images:
Wikimedia Commons (http://commons.wikimedia.org/wiki/Main_Page)
140 Brandeis Road
Newton, MA 02459
call: (617) 559-6561
nshslibrary@newton.k12.ma.us