spotlight.m

CSSearchableItemAttributeSet *attributeSet;
attributeSet = [[CSSearchableItemAttributeSet alloc] initWithItemContentType:(NSString *)kUTTypeImage];

attributeSet.title = @"Some Title";
attributeSet.contentDescription = @"Some Destiption";

attributeSet.keywords = @[@"Some", @"Keyword"];

UIImage *image = [UIImage imageNamed:@"someOptionalImage.png"];
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(image)];
attributeSet.thumbnailData = imageData;

CSSearchableItem *item = [[CSSearchableItem alloc] initWithUniqueIdentifier:@"com.company"
                                                           domainIdentifier:@"spotlight.myDomain"
                                                               attributeSet:attributeSet];

[[CSSearchableIndex defaultSearchableIndex] indexSearchableItems:@[item]
                                               completionHandler: ^(NSError * __nullable error) {
    if (!error) {
        NSLog(@"Search item indexed");
    }
}];