Open up your image into photoshop, duplicate your image in the layers window then goto “filter > artistic > poster edges”. Use standard settings, press ok. Then lighten the image abit by going to “image adjustments > brightness & contrast” increase the brighness by about 10-15 pixels and increase the contrast by about 25-30 pixels. (settings depends on type of image, lightness etc… you may not get the same result as mine)
Now goto “filter > artistic > cutout”. Here you will have to play around with the settings to archeve the right effect, here are the settings i used and my final result.
If you would like a more advanced way to cartoon, i suggest you try my tracing and cartooning tutorials.