C# controls.add from another class

Is the protection level of the PictureBox public? Other classes can only see objects that you allow them to.

[ADDED]

How about this.

public class players
{
    public PictureBox pb;

    public players()
    {
        this.pb = new PictureBox();
        this.pb.Image = Image.FromFile(@"D:\asd.jpg");
    }
}
public partial class Form1 : Form
{
    public Form1()
    {
            InitializeComponent();
            players p1 = new players();
            //Add control here. Controls.Add(p1.pb)
    }
}

modify your code as given below

public class players  
{
public PictureBox pb;
    public players()
    {
         pb = new PictureBox();
        pb.Image = Image.FromFile(@"D:\asd.jpg");
        //There I would like to add the control
    }
}
public partial class Form1 : Form
{
players  p1  // creating object of class because of this you can access any where inside this class(Form1)
    public Form1()
    {
            InitializeComponent();
            p1 = new players();
    }
    private void Form1_Load(object sender, EventArgs e)
       {
       p1.pb.Controls.Add(yourcontrol);  // Control.Add is accessible
       
      }

it will enable you to access what do you want.

I don't really understand why you would want to add a PictureBox from another class into your Form. If the PictureBox is to be shown on the Form it should belong to the Form and not any other class.

In the example code, the Players class should raise an event passing the path to the image, and the Form1 class should subscribe to the event and create the PictureBox from the path in the arguments.

Something like this:

using System;
using System.Drawing;
using System.IO;
using System.Windows.Forms;
public partial class Form1 : Form
{
    private Players players;
    public Form1()
    {
        InitializeComponent();
        players = new Players();
        players.NewPlayerImageRequest += new EventHandler<PathToImageEventArgs>(
            players_NewPlayerImageRequest);
        players.Initialize();
    }
    void players_NewPlayerImageRequest(object sender, PathToImageEventArgs e)
    {
        try
        {
            Image image = Image.FromFile(e.Path);
            PictureBox pictureBox = new PictureBox();
            pictureBox.Image = image;
            pictureBox.Size = image.Size;
            // Set other properties here
            Controls.Add(pictureBox);
        }
        catch (FileNotFoundException ex)
        {
            MessageBox.Show("The file " + ex.Message + " could not be found");
        }
        // catch other exceptions here
    }
}
public class Players
{
    public event EventHandler<PathToImageEventArgs> NewPlayerImageRequest;
    public const string DefaultImagePath = @"D:\asd.jpg";
    public void AddPlayerImage(string path)
    {
        OnNewPlayerImageRequest(new PathToImageEventArgs(path));
    }
    public void Initialize()
    {
        AddPlayerImage(DefaultImagePath);
    }
    protected virtual void OnNewPlayerImageRequest(PathToImageEventArgs e)
    {
        EventHandler<PathToImageEventArgs> eh = NewPlayerImageRequest;
        if (eh != null)
            eh(this, e);
    }
}
public class PathToImageEventArgs : EventArgs
{
    private string path;
    public PathToImageEventArgs(string path)
    {
        this.path = path;
    }
    public string Path
    {
        get { return path; }
    }
}