var imgSrc = '/captcha/125f38c45f312b5b6ffc0e8eea421d5b.png';
var code = '125f38c45f312b5b6ffc0e8eea421d5b';

document.getElementById('captcha').src = imgSrc;
document.getElementById('captcha').style.display = 'block';
document.getElementById('md5').value = code;