OSOLCaptcha 
Just have to follow 3 steps.
1.install the plugin
2.publish the plugin .
3.Check the 5 forms(mentioned above).
Though not required in most cases,we reccomend to go to admin page of the plugin and do the 2 addtional steps to enhance security against spam attacks ,they are
1.Set 'yes' for 'Enable second level security for Core forms' after making sure the captcha appears in all the above mentioned forms.(not needed from version 2.0 onwards)
If captcha doesnt appear in any of those forms(this will be due to template overrrides ),set 'No' to auto add feature for that particular form (otherwise that form wont work after enabling second level security check)
OR
Use the php block (mentioned in the documentation page )in the overridden template file of the form to have the captcha controls appear there
2.Further there is a layer of backend spam protection with the help of botscout api which could prevent even human spams to an extend.We reccomend you to enable this as well.
Can also be included with other joomla forms by putting the PHP block shown in the download page(this is different from version 2.0 onwards).For this you need to loacte the file that contains the html of the form.It is recommeded that this be done by coders or with their help though installing and publishing the plugin could be done by anyone(which in turn will add the captchs to the 3 forms mentioned above)
Currently there are 2 limitations for this plugin
1.If the html part is customized for com_user,mod_login or com_contact,it may not work.Since this is aimed for non techy joomla users it wont affect them as they dont edit any files
2.Enabling auto add for mod_login(not available from version 2.0 onwards) is subject to conditions and is disabled by default.if you enable it, make sure that it is in a unique position ,position must be any of these('left','right','top','user2','user3') .The position occupied by mod_login should not contain any other modules
I have included a link to the download page of this plugin with the captcha image.You are free to remove it,though I will be happy to have that link with the captcha image :)
This is my first extension to JED.Any suggestions and help on improving this plugin will be much appreciated
PS:Please check the technical requirements section and FAQs section in the download page of the plugin,first if you are having any issues with the plugin
AJAX verification introduced in version 2.0 beta so that form data is not lost on submission due to wrong captcha value.Coders/developrs are requested to check this and mail feedback
Feel free to post your doubts,suggestions,reccomendations and any issues with this plugin thorugh contact us form in my site
Gave it a "Good" rating because it is a bit difficult customizing the layout, maybe the dev can create a separate template file?
Good plugin nonetheless.
But since spammers do not use the form itself and rather send data directly to the correspondent script, it's rather useless. Sending data to "task=register_save" without the captcha variables still will enable spammers to create useless accounts.
You are writing as if you have found something new.the issue was reported within 2 weeks of beta testing(seven months past now) and solution was incorporated with 2 addtional options on version 1.0.3(secondlevel security and botscout options) on enabling which all kind of bot spams are prevented.This includes the one you have mentioned(sending data to "task=register_save" without the captcha variables).Anyway next time when you make these type of 'announcements' try to read the documentation and apply it completely or contact developers before doing so instead of claiming an age old discovery as yours
One site was good to go after publishing the plugin.
Second site needed some work as it had template overrides, but just placed the code in the override contact form and set the auto add to contact form in the plugin to no and it worked like a charm as well.
I love it that you don't have to hack core files. Saves so much trouble after upgrading....
thanks for this plugin!
We started getting spambot attempts through our Contact forms. None of the mail actually got through due to the nonexistent "from" addresses, but still, lots of junk mail with which I had to deal.
I installed OSOLCaptcha to try to handle the form-generated Spam. This extension works PERFECTLY, and with very little configuration. A little added CSS for styling and I was done. So far, we are down to about 1 spam attempt every few days; I suspect these are coming from humans.
Kudos to the developer for something simple, elegant and easy to implement!
After disabling the BotScout function, it worked like a charme. But i lost hours to find the mistake.
although this captcha is installed and set to highest level I have spam accounts registering in my forum , maybe 10 per day.
I will have to try another one now.
If you have any issues you should have contacted us first 'properly'.There was an enquiry with this same subject,but I am not sure wether it was you .The site url wasnt given as well as the email given was wrong(it bounced when we replied asking the url).Such enquiries doesnt serve any purpose with doors closed for communication.If you have any issues sharing your email id,please use the forum for this plugin, before blaming the software based on your own 'conclusions'
Many thanks to the developers, this is the sort of simple to use plugin which makes Joomla so easy to implement and maintain, above all others.
From what I've seen, the author looks at software from a "user-friendly" perspective, and works hard to accomplish both functionality and eash of use.
no hacks no fuss.
All my captcha problems solved, spent 2 days trying numerous other solutions and managed to solve all captcha issues in 20 minutes using this plugin.
2 thumbs up from me, thank you very much
Not sure how to reply this frivolous remark.If there is some genuine issue , you need to either contact us or post it in the forum http://forum.joomla.org/viewtopic.php?p=2072414#p2072414 prior deriving your own conclusions and pouncing hastily to write something like this.Anybody can make a remark here like this and there is no way to know what exactly is wrong unless you elaborate your issue with references.One thing I can say for sure is that after you enable second level security and botscout options,not bot spams will pass through it.Botsout protection will also protect human spam to an extend and is available for some components beyond core joomla forms with form field named 'email' for eg:virtuemart registration.
It is always recommended to read the documentation and forum completely as is the case of any piece of software.Don't put the blame on developers for your ignorance