In order to install it on your pi follow the steps:
1. Install subversion:
sudo apt-get update
sudo apt-get install subversion

2. Go to the folder where you want to have the mjpg-stremer, for example /home/pi
cd /home/pi

3. Get mjpg-streamer:
sudo svn co https://svn.code.sf.net/p/mjpg-streamer/code/mjpg-streamer  mjpg-streamer

4. Install libjpeg8-dev
sudo apt-get install libjpeg8-dev

5. Install ImageMagick
sudo apt-get install imagemagick

6. Make the project:
cd mjpg-streamer/mjpg-streamer
make

7. When it finishes you should be ready to start streaming your video. To do so, enter the following command:
./mjpg_streamer -i "./input_uvc.so" -o "./output_http.so -w ./www"

8. Now you should be able to view the stream from other computer on your network. Open a web browser and open the following link:
http://{name or IP-address of the Raspi}:8080

9. However, to let the stream be viewed from outsite your network you will need to port forward your router. This varies from router to router, so please search on google how to do it on yours.

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sudo svn co https://svn.code.sf.net/p/mjpg-streamer/code/mjpg-streamer  mjpg-streamer