When you create a custom Windows or Web control, compile it and add it to the Visual Studio .NET's Toolbox, the control is added to the toolbox with a default bitmap representing a gear. This might be fine if you're developing the controls for your own use, but it surely isn't what you want if you're developing commercial components. In that case you want to associate a custom bitmap to the custom controls, so that the user can recognize them among the others more easily, and so that they look more professional.
Here are the steps to follow to show a custom bitmap when you add your controls to the Toolbox:
1) Create a 16x16 bitmap of 16 colors. The color of the bottom-left corner is used as a transparent color.
2) Add the bitmap to the Web/Windows Custom Control project, and set its Build Action to Embedded Resource.
3) Add the ToolboxBitmap to the custom control class, as shown below:
If the bitmap has the same name of the custom control class (it should be MyUserControl.bmp in this case) you can even avoid the second parameter in the ToolboxBitmapAttribute's constructor, as follows:
<ToolboxBitmap(GetType(MyUserControl), "MyCustomCtl.bmp")> Public Class _
<ToolboxBitmap(GetType(MyUserControl))> Public Class MyUserControl