How to minimize Image size less then 200kb

Many of the online application forms request less then 200kb or 100kb  image.today i tell solution for that
Memory size of Image is based on the pixel or resolution.you decrease the pixel or resolution means the image size also decrease.Using windows paint you can minimize your photo size

Note:
It can applicable for video also.In video conversion settings(video converter settings) optimize the resolution and audio encoding you can minimize the video size