Sample of PhotoKit on macOS.

randaom256x256.m

//To Compile: cc -fobjc-arc -framework Cocoa -framework Photos random256x256.m -o random256x256
#import <Cocoa/Cocoa.h>
#import <Photos/Photos.h>
#include <stdlib.h>

int main()
{
    @autoreleasepool{
        PHFetchResult *assets = [PHAsset fetchAssetsWithMediaType: PHAssetMediaTypeImage options: nil];
        NSUInteger idx = arc4random() % assets.count;
        PHAsset *asset = assets[idx];
        PHImageManager *phiManager = [PHImageManager defaultManager];
        PHImageRequestOptions *opt = [[PHImageRequestOptions alloc] init];
        opt.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;
        opt.resizeMode = PHImageRequestOptionsResizeModeExact;
        // PHImageRequestOption's synchronous blocks the thread until data is ready.
        // So we don't need RunLoop.
        // (If opt.synchronous is NO (default), we need RunLoop to wait until resultHandler completes.)
        opt.synchronous = YES;
        [phiManager requestImageForAsset: asset
            targetSize: CGSizeMake(256,256)
            contentMode: PHImageContentModeAspectFill
            options: opt
            resultHandler: ^(NSImage *resultImage, NSDictionary *info){
                NSBitmapImageRep *bitmap = [NSBitmapImageRep imageRepWithData: [resultImage TIFFRepresentation]];
                NSData *jpegData = [bitmap representationUsingType: NSBitmapImageFileTypeJPEG properties: [NSDictionary dictionary]];
                NSFileHandle *fh = [NSFileHandle fileHandleWithStandardOutput];
                [fh writeData: jpegData];
            }
        ];
    }
    return 0;
}