It's a tricky one, I'm currently building my directory clickfound, it's been an ongoing project for a little while. It's a directory of website designers. It didn't previously require a reciprocal link but it seems that requiring this is the only way that seems to 100% prevent bogus signups - I receive hundreds of random signups for everything but website designers at the moment. Do you think that people are fed of up reciprocal directories and are so avoiding it? It's a PR4 directory which I would have thought would entice signups. Then you get onto paid links - these are the most successful directories it would seem but why? I want to create a useful resource of website designers, but it seems that the decision I make now will affect the sites future.
Maybe the links submitted to your directory are done by software. Change it to reciprocal or paid link will not solve the problem. My directory, http://directory.gtsee.com, which is image verification enabled, still gets around 500 submissions per day, and almost 99% of the links are spam and submitted by automatic software.
Are people really going to put directory reciprocal links all over their sites? No. If you have a nice site you work on every week it has custom graphics etc then you are going to paste ghetto directory links all over it? Turn a sidebar into a mini link farm? Not A directory doesn’t have that much to offer.. In SEO directories are not that important you have a link mixed with thousands of irrelevant links. So a lot of webmasters usually put the site in a hundred or so directories a year, mostly just because they are there. People won't put links on their site just to get into another directory. They just got listed in 20 yesterday 150 the week before and now this one wants them to put a link on their page?
Requiring a link in return for a listing is deemed to be a "link scheme" by Google. This is not a good idea. My recommendation would be to start out as a paid directory. You will not earn much revenue when you start, but you can focus on adding your own listings - thus making sure your directory becomes a high quality resource. Good luck!
Reciprocal directories were past looooong time before i would say, it's absolutely a very poor, bad, useless and dangerous idea, since you never no which "good/healthy" sites link to you. How cool?
In addition to image verification code, you can also implement email validation. Once URL was submitted, your system will automatically send verification email to provided email address and activation link. This process requires manual intervention to activate the listing. As well you can add cap on number of websites listed per email and you can require email from that domain only, not @gmail.com, no @yahoo.com and any other public emails services.