Make an embedded image which can be zoomed into. 

http://closr.it

Make a palette of colors based on an image.

http://palettefx.com/

Paint your picture... COULD have inappropriate images by others...

http://www.psykopaint.com/painter.html

Photovisi

Probably best for Teacher (gallery could have questionable images from others)

http://www.photovisi.com/