Swift で UIImage の方向を強制的に変換する ref: http://qiita.com/kitsuyui/items/c8d76acfa0ecd6570fdb

UIImage+fixOrientation.swift

//
//  UIImage+fixOrientation.swift
//

import UIKit

extension UIImage {
    func fixOrientation () -> UIImage {
        if self.imageOrientation == UIImageOrientation.Up {
            return self
        }
        var transform = CGAffineTransformIdentity
        typealias o = UIImageOrientation
        let width = self.size.width
        let height = self.size.height

        switch (self.imageOrientation) {
        case o.Down, o.DownMirrored:
            transform = CGAffineTransformTranslate(transform, width, height)
        case o.Left, o.LeftMirrored:
            transform = CGAffineTransformTranslate(transform, width, 0)
            transform = CGAffineTransformRotate(transform, CGFloat(M_PI_2))
        case o.Right, o.RightMirrored:
            transform = CGAffineTransformTranslate(transform, 0, height)
            transform = CGAffineTransformRotate(transform, CGFloat(-M_PI_2))
        default: // o.Up, o.UpMirrored:
            break
        }

        switch (self.imageOrientation) {
        case o.UpMirrored, o.DownMirrored:
            transform = CGAffineTransformTranslate(transform, width, 0)
            transform = CGAffineTransformScale(transform, -1, 1)
        case o.LeftMirrored, o.RightMirrored:
            transform = CGAffineTransformTranslate(transform, height, 0)
            transform = CGAffineTransformScale(transform, -1, 1)
        default: // o.Up, o.Down, o.Left, o.Right
            break
        }
        let cgimage = self.CGImage

        let ctx = CGBitmapContextCreate(nil, UInt(width), UInt(height),
                CGImageGetBitsPerComponent(cgimage), 0,
                CGImageGetColorSpace(cgimage),
                CGImageGetBitmapInfo(cgimage))
        switch (self.imageOrientation) {
        case o.Left, o.LeftMirrored, o.Right, o.RightMirrored:
            CGContextDrawImage(ctx, CGRectMake(0, 0, height, width), cgimage)
        default:
            CGContextDrawImage(ctx, CGRectMake(0, 0, width, height), cgimage)
        }
        let cgimg = CGBitmapContextCreateImage(ctx)
        let img = UIImage(CGImage: cgimg)
        return img!
    }
}