tasks. Rather than users actively participating in solving a problem or providing information, implicit crowdsourcing involves users doing another task entirely where a third party gains information for another topic based on the user's actions. A good example of implicit crowdsourcing is the ESP game, where users find words to describe Google images, which are then used as metadata for the images. Another popular use of implicit crowdsourcing is through reCAPTCHA, which asks people to solve CAPTCHAs to prove they are human, and then provides CAPTCHAs from old books that cannot be deciphered by computers, to digitize them for the web. Like many tasks solved using the Mechanical Turk, CAPTCHAs are simple for humans, but often very difficult for computers. Piggyback crowdsourcing can be seen most frequently by websites such as Google that data-mine a user's search history and websites to discover keywords for ads, spelling corrections, and finding synonyms. In this way, users are unintentionally helping to modify existing systems, such as Google Ads. Other types Creative crowdsourcing involves sourcing people for creative projects such as graphic design, crowdsourcing architecture, product design, apparel design, movies, writing, company naming, illustration, etc. While crowdsourcing competitions have been used for decades in some creative fields such as architecture, creative crowdsourcing has proliferated with the recent development of web-based platforms where clients can solicit a wide variety of creative work at lower cost than by traditional means. Crowdshipping (crowd-shipping) is a peer-to-peer shipping service, usually conducted via an online platform or marketplace. There are several methods that have been categorized as crowd-shipping: Travelers heading in the direction of the buyer, and are willing to bring the package as part of their luggage for a reward. Truck drivers whose route lies along the buyer's location and who are willing to take extra items in their truck. Community-based platforms that connect international buyers and local forwarders, by allowing buyers to use forwarder's address as purchase destination, after which forwarders ship items further to the buyer. Crowdsolving is a collaborative and holistic way of solving a problem through many people, communities, groups, or resources. It is a type of crowdsourcing with focus on complex and intellectually demanding problems requiring considerable effort, and the quality or uniqueness of contribution. Problem–idea chains are a form of idea crowdsourcing and crowdsolving, where individuals are asked to submit ideas to solve problems and then problems that can be solved with