How decaptcher works ?

I would like to know how services like decaptcher works ?
Will the captcha generated on our screens be uploaded to their servers
and people behind these solvers solve it for us ?
If so how are the images being uploaded without our concern ?
how do I code something similar in php(so examples)
so that I can get someone to solve
my captcha's while I concentrate on other works ?

just look em up. they have example code in PHP

It is not uploaded automatically. You have to send it to them via one of the APIs or code your own. Its on their website