Many classroom interaction researchers struggle with blurring their participants’ faces in the images that will be used for publications and presentations.
I am sure there are thousands of easier ways, but I use GIMP, a free image editing software that works both on MAC and Windows. I created a gif explaining the process. I hope it helps.
Olcay Sert 
thank you, very useful indeed! and a very young sert teaching here 😉
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