ALAssetRepresentation *assetRep = [asset defaultRepresentation];
NSString *mediaType = [assetRep UTI];

#import <ImageIO/ImageIO.h>
- (NSString *)infoFromImageIO:(ALAssetRepresentation *)assetRep
{NSMutableData *imgData = nil;NSString *mediaType = [assetRep UTI];// create a buffer to hold image datauint8_t *buffer = (Byte*)malloc(assetRep.size);NSUInteger length = [assetRep getBytes:buffer fromOffset:0.0  length:assetRep.size error:nil];if (length > 0){imgData = [[NSMutableData alloc] initWithBytesNoCopy:buffer length:length freeWhenDone:YES];}// identify image type (jpeg, png, RAW file, ...) using UTI hintNSDictionary* sourceOptionsDict = [NSDictionary dictionaryWithObjectsAndKeys:(id)[assetRep UTI] ,kCGImageSourceTypeIdentifierHint,nil];// create CGImageSource with NSDataCGImageSourceRef sourceRef = CGImageSourceCreateWithData((CFDataRef)imgData,  ( CFDictionaryRef) sourceOptionsDict);// get imagePropertiesDictionary
    CFDictionaryRef imagePropertiesDictionary;imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex(sourceRef,0, NULL);// get exif dataCFDictionaryRef exif = (CFDictionaryRef)CFDictionaryGetValue(imagePropertiesDictionary, kCGImagePropertyExifDictionary);NSDictionary *exif_dict = (NSDictionary*)exif;if (exif_dict && [exif_dict count] > 0){//获取创建时间NSString *createTime = [NSString stringWithString:[exif_dict objectForKey:@"DateTimeOriginal"]];CFRelease(imagePropertiesDictionary);CFRelease(sourceRef);return createTime;}return nil;
#if 0// save image WITH meta dataNSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];NSURL *fileURL = nil;CGImageRef imageRef = CGImageSourceCreateImageAtIndex(sourceRef, 0, imagePropertiesDictionary);if (![[sourceOptionsDict objectForKey:@"kCGImageSourceTypeIdentifierHint"] isEqualToString:@"public.tiff"]){fileURL = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@.%@",documentsDirectory,@"myimage",[[[sourceOptionsDict objectForKey:@"kCGImageSourceTypeIdentifierHint"] componentsSeparatedByString:@"."] objectAtIndex:1]]];CGImageDestinationRef dr = CGImageDestinationCreateWithURL ((__bridge CFURLRef)fileURL,(__bridge CFStringRef)[sourceOptionsDict objectForKey:@"kCGImageSourceTypeIdentifierHint"],1,NULL);CGImageDestinationAddImage(dr, imageRef, imagePropertiesDictionary);CGImageDestinationFinalize(dr);CFRelease(dr);}else{NSLog(@"no valid kCGImageSourceTypeIdentifierHint found …");}// clean up
    CFRelease(imageRef);CFRelease(imagePropertiesDictionary);CFRelease(sourceRef);
#endif
}