部分代码：

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library assetForURL:[info objectForKey:UIImagePickerControllerReferenceURL]
    resultBlock:^(ALAsset *asset) {
        @strongify(filePath)
        @strongify(imagePath)
        @strongify(photoName)
        ALAssetRepresentation *representation = [asset defaultRepresentation];
                 
        NSLog(@"size of asset in bytes: %lld", [representation size]);

        Byte *buffer = (Byte*)malloc(representation.size);
        NSUInteger buffered = [representation getBytes:buffer fromOffset:0.0 length:representation.size error:nil];
        NSData *imgData = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];
                 
        NSLog(@"imagePath === %@", imagePath);
        NSLog(@"photoName === %@", photoName);
                 
        if ([[self typeForImageData:imgData] isEqualToString:@"image/gif"]) {
            NSLog(@"GIF image");
            filePath = [imagePath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.gif", photoName]];
            NSLog(@"filePath 3 === %@", filePath);
            [imgData writeToFile:filePath atomically:YES];
            NSLog(@"Check === %d", [imgData writeToFile:filePath atomically:YES]);
        } else {
            NSLog(@"not GIF image");
            filePath = [imagePath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.jpg", photoName]];
            NSLog(@"filePath 4 === %@", filePath);
                     
            CGRect rect = CGRectMake(0, 0, 750, 750 / image.size.width *image.size.height);
            UIGraphicsBeginImageContext( rect.size );
            [image drawInRect:rect];
            UIImage *picture = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
            [UIImageJPEGRepresentation(picture, 1) writeToFile:filePath atomically:YES];
        }
        NSLog(@"photoName 1 === %@", photoName);
        [self.wkWebView evaluateJavaScript:[NSString stringWithFormat:@"%@(%@)", [ConfigHelper getStringValueForKey:@"uploadImageIdMethod"], photoName] completionHandler:nil];
    }
    failureBlock:^(NSError *error) {
        NSLog(@"couldn't get asset: %@", error);
        [self showHud:@"图片上传有误！"];
    }
];