It's possible to change the behavior of Winforms controls with regard to UI Automation. If you want a PictureBox to be seen as a button by UI Automation, and therefore be clickable using UI Automation tools, you can derive from PictureBox and override Automation/Accessible methods, something like this:

Before:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        var pb = new PictureBox();
        pb.Dock = DockStyle.Fill;
        pb.Click += (s, e) => MessageBox.Show("hello world");
        Controls.Add(pb);
    }
}

This is how Inspect (from the SDK tools) sees it, as a "pane", with no specific action:

After:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        var pb = new ButtonPictureBox();
        pb.Dock = DockStyle.Fill;
        pb.Click += (s, e) => MessageBox.Show("hello world");
        Controls.Add(pb);
    }
}

public class ButtonPictureBox : PictureBox
{
    protected override AccessibleObject CreateAccessibilityInstance() => new Accessible(this);

    private class Accessible : ButtonBase.ButtonBaseAccessibleObject
    {
        public Accessible(ButtonPictureBox control)
            : base(control)
        {
        }

        public new ButtonPictureBox Owner => (ButtonPictureBox)base.Owner;
        public override AccessibleRole Role => AccessibleRole.PushButton;
        public override AccessibleStates State => AccessibleStates.Default;
        public override void DoDefaultAction() => Owner.OnClick(EventArgs.Empty);
    }
}

Now, Inspect sees it as a "button" and the Invoke Pattern is available, so if you Invoke it, the Click method will be raised: