Create a good file of all images that you think would make fun or good cartoons. The images can be personal picture of you and your friends, other ideas can be turning pictures of your pets into cartoons. Whatever the case may be, make sure to store all your images that you want to turn into cartoon in one place.
Make sure the image files that you selected are compatible with the online "photo into cartoon" company that you choose to use. Make of the companies online that offer to turn photos into cartoon will have a specific file type and size that they require.
I would recommend trying a variety of online companies that turn photos into cartoons because each of them will have a slightly different technology and final image cartoon. You can then select which type of cartoon you like best. Some companies will require a fee, but other will be free online companies that turn photos into cartoons.