How can I save an image to the camera roll?

You use the UIImageWriteToSavedPhotosAlbum() function.

//Let's say the image you want to save is in a UIImage called "imageToBeSaved"UIImageWriteToSavedPhotosAlbum(imageToBeSaved, nil, nil, nil);

Edit:

//ViewController.m- (IBAction)onClickSavePhoto:(id)sender{    UIImageWriteToSavedPhotosAlbum(imageToBeSaved, nil, nil, nil);}

Here's an answer for iOS8+ using the Photos framework.

Objective-C:

#import <Photos/Photos.h>UIImage *snapshot = self.myImageView.image;[[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{    PHAssetChangeRequest *changeRequest = [PHAssetChangeRequest creationRequestForAssetFromImage:snapshot];    changeRequest.creationDate          = [NSDate date];} completionHandler:^(BOOL success, NSError *error) {    if (success) {        NSLog(@"successfully saved");    }    else {        NSLog(@"error saving to photos: %@", error);    }}];

Swift:

// Swift 4.0import Photoslet snapshot: UIImage = someImagePHPhotoLibrary.shared().performChanges({    PHAssetChangeRequest.creationRequestForAsset(from: snapshot)}, completionHandler: { success, error in    if success {        // Saved successfully!    }    else if let error = error {        // Save photo failed with error    }    else {        // Save photo failed with no error    }})

Here's a link to the Apple documentation.

Don't forget to add the appropriate key/value to your info.plist to request permission to access the photo library:

<key>NSCameraUsageDescription</key><string>Enable camera access to take photos.</string><key>NSPhotoLibraryUsageDescription</key><string>Enable photo library access to select a photo from your library.</string><key>NSPhotoLibraryAddUsageDescription</key><string>Enable photo library access to save images to your photo library directly from the app.</string>

For reference, you can save videos in a similar manner:

UISaveVideoAtPathToSavedPhotosAlbum(videoPath, nil, nil, nil);

You might want to save a video to upload to Instagram, for example:

// Save video to camera roll; we can share to Instagram from there.-(void)didTapShareToInstagram:(id)sender {     UISaveVideoAtPathToSavedPhotosAlbum(self.videoPath, self, @selector(video:didFinishSavingWithError:contextInfo:), (void*)CFBridgingRetain(@{@"caption" : caption}));}- (void)               video: (NSString *) videoPath    didFinishSavingWithError: (NSError *) error                 contextInfo: (void *) contextInfoPtr {    NSDictionary *contextInfo = CFBridgingRelease(contextInfoPtr);    NSString *caption         = contextInfo[@"caption"];    NSString *escapedString   = [videoPath stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLHostAllowedCharacterSet]]; // urlencodedString    NSString *escapedCaption  = [caption stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLHostAllowedCharacterSet]]; // urlencodedString    NSURL *instagramURL       = [NSURL URLWithString:[NSString stringWithFormat:@"instagram://library?AssetPath=%@&InstagramCaption=%@", escapedString, escapedCaption]];    [[UIApplication sharedApplication] openURL:instagramURL];}