Tumblr: post random image

I am looking for information on how to do a random automation post for tumblr. Maybe it already exists.

I will like to put all my pictures in a folder ( on my computer or on my server) and on time a day or one time a week the script chose a random image and post it on my tumbler and after that it dealet the image on the folder. I can always add images to the folder when I have new one.

Did someone know something similar that si buld? Any idea on how to start doing this ? I imagine it will be with the api.