Using a camera and a blog to get students writing explanations

I believe someone only really understands something when they can explain it. My "ah-ha" moment with this happened when I was explaining "reverse faulting" and at the blackboard understood what it was!
Today I will get my year 11 horticulture students to write an explanation of how to sow seeds indoors. I will demonstrate this. Give them some photos of each step. Ask them to sequence the photos then write what each photo is showing then put these on a class blog.