效果如下，下载地址：上传太慢，改天吧。。

验证码效果的实现代码

import UIKit

class CodeView: UIView
{
    
    var changeString:String? //验证码的字符串
    
    let kLineCount = 6
    let kLineWidth = CGFloat(2.0)
    let kCharCount = 4
    let kFontSize = UIFont.systemFontOfSize(CGFloat(arc4random() % 5) + 18)

    override init(frame: CGRect)
    {
        super.init(frame: frame)
        let randomColor:UIColor = UIColor(red: CGFloat(CGFloat(random())/CGFloat(RAND_MAX)),green: CGFloat(CGFloat(random())/CGFloat(RAND_MAX)),blue: CGFloat(CGFloat(random())/CGFloat(RAND_MAX)),alpha: 0.5)
        
        self.layer.cornerRadius = 5.0   //设置layer圆角半径
        self.layer.masksToBounds = true //隐藏边界
        self.backgroundColor = randomColor
        
        self.getChangeCode()
    }

    required init(coder aDecoder: NSCoder)
    {
        super.init(coder: aDecoder)!
        self.getChangeCode()
    }
    
    func getChangeCode()
    {
        //字符素材数组
        let changeArray:NSArray = ["0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
        
        self.changeString = ""
        //随机从数组中选取需要个数的字符，然后拼接为一个字符串
        for(var i=0;i<kCharCount;i++)
        {
            let index = Int(arc4random())%(changeArray.count - 1)
            let getStr = changeArray.objectAtIndex(index)
            self.changeString = self.changeString! + (getStr as! String)
        }
        print("验证码：\(changeString)")
    }
    
    override func touchesBegan(touches: Set<UITouch>,withEvent event: UIEvent?)
    {
        super.touchesBegan(touches,withEvent: event)
        getChangeCode()
        setNeedsDisplay()
        
    }
    
    override func drawRect(rect: CGRect)
    {
        super.drawRect(rect)
        let randomBackColor = UIColor(red: CGFloat(CGFloat(random())/CGFloat(RAND_MAX)),alpha: 1.0)
        self.backgroundColor = randomBackColor
        
        //获得要显示验证码字符串，根据长度，计算每个字符显示的大概位置
        let str = NSString(string: "S")
//        let font = UIFont.systemFontOfSize(20)
        let size = str.sizeWithAttributes([NSFontAttributeName : kFontSize])
        let width = rect.size.width / CGFloat(NSString(string: changeString!).length) - size.width
        let height = rect.size.height - size.height
        var point:CGPoint?
        var pX:CGFloat?
        var pY:CGFloat?
        
        for(var i=0;i<NSString(string: changeString!).length;i++)
        {
            pX = CGFloat(arc4random()) % width + rect.size.width / CGFloat(NSString(string: changeString!).length)*CGFloat(i)
            pY = CGFloat(arc4random()) % height
            point = CGPointMake(pX!,pY!)
            let c = NSString(string: changeString!).characterAtIndex(i)
            
            let codeText:NSString? = NSString(format: "%C",c)
            codeText!.drawAtPoint(point!,withAttributes: [NSFontAttributeName : kFontSize])
        }
    
        //调用drawRect：之前，系统会向栈中压入一个CGContextRef，调用UIGraphicsGetCurrentContext()会取栈顶的CGContextRef
        let context :CGContext = UIGraphicsGetCurrentContext()!
        //设置画线宽度
        CGContextSetLineWidth(context,kLineWidth)
        
        for(var i=0;i<kLineCount;i++)
        {
            //绘制干扰的彩色直线
            let randomLineColor = UIColor(red: CGFloat(CGFloat(random())/CGFloat(RAND_MAX)),alpha: 0.5)
            CGContextSetStrokeColorWithColor(context,randomLineColor.CGColor)
            //设置线的起点
            pX = CGFloat(arc4random()) % rect.size.width
            pY = CGFloat(arc4random()) % rect.size.height
            CGContextMoveToPoint(context,pX!,pY!)
            //设置线终点
            pX = CGFloat(arc4random()) % rect.size.width
            pY = CGFloat(arc4random()) % rect.size.height
            CGContextAddLineToPoint(context,pY!)
            //画线
            CGContextStrokePath(context)
        }
    }

}

不区分大小写验证的代码实现

        let str1 = textField.text
        let str2 = codeView.changeString
        
        let result = str1!.rangeOfString(str2!,options: NSStringCompareOptions.CaseInsensitiveSearch)
        if(result == nil) //验证码不正确
        {
            let alert = UIAlertView(title: nil,message: "验证码错误",delegate: self,cancelButtonTitle: "确定")
            alert.show()
        }
        else
        {
            let alert = UIAlertView(title: nil,message: "验证码正确",cancelButtonTitle: "确定")
            alert.show()
        }