I first came across the idea of crowdsourcing a few years ago through Sitepoint’s Contests section.
If you haven’t come across the concept of crowdsourcing, basically, the idea is that an individual or organisation (aka contest holder) who needs a design job done (a logo, web design, etc) can post a contest and designers can take part in it by submitting their own designs on spec. The contest holder will then choose from the submitted designs and award a prize (usually, in cash) to the winner.
This concept has been applauded by people who are looking for an alternative way to obtain design jobs and/or to get some options in completing desired design. From a designer point of view, those who aren’t getting enough jobs (or just starting to build their portfolios), may see this as a good way to make some extra cash and gain some extra exposure/experience. From a client point of view, it makes the process of finding reasonably-priced design work completed a lot easier and simpler. Plus, clients get the option of choosing from varied designer styles and experiences.
However, there are also several designers look down on this type of work. Many think that this de-values the work of designers in general. And, it provides a lot of scope for plagiarism/copyright infringement. There are many other complaints about crowdsourcing from a few professionals in this field.
In any case, if you’re a designer who wish to find ways to make some money doing crowdsourcing work, two of the most popular places that I’m aware of at the moment are:

- 99Designs – This is basically the old Sitepoint contests section. The guys from Sitepoint obviously saw a need to expand this area, so 99Designs was born. There are several design contests going on all the time in this site.

- Crowdspring – This is another popular design marketplace online. Over a hundred design specs going at any given time. Clients can also browse designer portfolios in a nice, simple manner.
I haven’t participated in crowdsourcing yet myself as an individual. However, I know a few people who got their logos, web designs, and graphic design needs through crowdsourcing and they seem happy with the process and outcome.
What about you? Have you tried crowdsourcing before – either as a contest holder or as a designer? If yes, how did it all go? Will you recommend it? If not, why not?