Saving image from url using Picasso?

I Modified the solution to this, adding permissions and a button to load and save the Image,and PhotoLoader class remains the same !

private static final String[] STORAGE_PERMISSIONS = { Manifest.permission.WRITE_EXTERNAL_STORAGE};
    ImageView imageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageView = (ImageView) findViewById(R.id.imageView);

        verifyPermissions();
    }
    public void save(View view)
    {
        Picasso.with(this)
                .load("https://www.w3schools.com/howto/img_fjords.jpg")
                .into(new PhotoLoader("myImg.jpg" , imageView));
    }

    public void verifyPermissions()
    {
        // This will return the current Status
        int permissionExternalMemory = ActivityCompat.checkSelfPermission(MainActivity.this,Manifest.permission.WRITE_EXTERNAL_STORAGE);

        if(permissionExternalMemory != PackageManager.PERMISSION_GRANTED)
        {
            // If permission not granted then ask for permission real time.
            ActivityCompat.requestPermissions(MainActivity.this,STORAGE_PERMISSIONS,1);
        }
    }

Solved. now works fine!

I did

//save image
    public static void imageDownload(Context ctx, String url){
        Picasso.with(ctx)
                .load("http://blog.concretesolutions.com.br/wp-content/uploads/2015/04/Android1.png")
                .into(getTarget(url));
    }

    //target to save
    private static Target getTarget(final String url){
        Target target = new Target(){

            @Override
            public void onBitmapLoaded(final Bitmap bitmap, Picasso.LoadedFrom from) {
                new Thread(new Runnable() {

                    @Override
                    public void run() {

                        File file = new File(Environment.getExternalStorageDirectory().getPath() + "/" + url);
                        try {
                            file.createNewFile();
                            FileOutputStream ostream = new FileOutputStream(file);
                            bitmap.compress(Bitmap.CompressFormat.JPEG, 80, ostream);
                            ostream.flush();
                            ostream.close();
                        } catch (IOException e) {
                            Log.e("IOException", e.getLocalizedMessage());
                        }
                    }
                }).start();

            }

            @Override
            public void onBitmapFailed(Drawable errorDrawable) {

            }

            @Override
            public void onPrepareLoad(Drawable placeHolderDrawable) {

            }
        };
        return target;
    }

I can see 2 possible issues:

1. trying to save to external storage without write permissions in your manifest
2. try change the filename so its not the whole url, which could be your issue because of the characters in your url that arent valid as filename chars.