Black and white:
FREE chalk: http://www.teacherspayteachers.com/Product/School-Supplies-Chalk-Clip-Art-1389992
Use these to create all sorts of materials for your students! Or, if you create to sell a digital item, please be sure my images make up less than 33% of your item, that your preview images are either low resolution or watermarked, and the purchased files are flattened. Crediting me is wonderful and so appreciated, but not required.