如何引用两种模糊方法

Question

编译项目时遇到问题：两个代码的模糊引用

Image img = pictureBox1.Image.Crop(_selection); 

和

pictureBox1.Image = img.Fit2PictureBox(pictureBox1); 

分别是错误的

Error   1   The call is ambiguous between the following methods or properties: 
'gfoidl.Imaging.ImageExtension.Crop(System.Drawing.Image, System.Drawing.Rectangle)' and 
'gfoidl.Imaging.ImageExtension.Crop(System.Drawing.Image, System.Drawing.Rectangle)'    E:\2012-11 (Nov)\Cropping of Images\Form1.cs    76  29  Cropping of Images
Error   2   The call is ambiguous between the following methods or properties: 
'gfoidl.Imaging.ImageExtension.Fit2PictureBox(System.Drawing.Image, System.Windows.Forms.PictureBox)' and
'gfoidl.Imaging.ImageExtension.Fit2PictureBox(System.Drawing.Image, System.Windows.Forms.PictureBox)'   E:\2012-11 (Nov)\Cropping of Images\Form1.cs    79  25  Cropping of Images  


private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left && _selecting)
    {
        // Create cropped image:
        Image img = pictureBox1.Image.Crop(_selection);

        // Fit image to the picturebox:
        pictureBox1.Image = img.Fit2PictureBox(pictureBox1);

        _selecting = false;
    }
}

如果你能告诉我如何引用那些没有含糊不清的内容