How to make Picture Box in C# transparent is very simple.

pictureBox1.BackColor = Color.Transparent;
pictureBox1.BringToFront();

If you still don't see it transparent then probably it is picking up the color from the background form or another control.

If it is form then you may have to make it also transparent.
If it is picture box over another picture box then you will have to set this control child of that control.

Example
pictureBox1.Parent = pictureBox2;

How to make Picture Box in C# transparent is very simple.

pictureBox1.BackColor = Color.Transparent;
pictureBox1.BringToFront();

If you still don't see it transparent then probably it is picking up the color from the background form or another control.

If it is form then you may have to make it also transparent.
If it is picture box over another picture box then you will have to set this control child of that control.

Example
pictureBox1.Parent = pictureBox2;