I believe in Taobao, betta these big sites have seen such a verification code, drag the verification code than the traditional mobile side has a better test to reduce the user's input. Verification code: third party charges drag code, betta, panda live and many other sites are using this verification code. Or the charges. I feel very strange, such a large site, actually this function should use a third party, it should be no difficulties to achieve it, so I would like to do with php + js to do the same function, the name is called tncode it, 39 verification code, ha ha! The main technology to achieve: 1, php cutout 2, js canvas drawing 3, crack interference