c# – 文件正忙.我无法删除它

public static void SetImageCopyright(string imageFile)
        {
            #region 
            //create a image object containing the photograph to watermark
            Image imgPhoto = Image.FromFile(imageFile);
            int phWidth = imgPhoto.Width;
            int phHeight = imgPhoto.Height;

            //create a Bitmap the Size of the original photograph
            Bitmap bmPhoto = new Bitmap(phWidth,phHeight,PixelFormat.Format24bppRgb);

            bmPhoto.SetResolution(imgPhoto.HorizontalResolution,imgPhoto.VerticalResolution);

            //load the Bitmap into a Graphics object 
            Graphics grPhoto = Graphics.FromImage(bmPhoto);


            //------------------------------------------------------------
            //Step #1 - Insert Copyright message
            //------------------------------------------------------------

            //Set the rendering quality for this Graphics object
            grPhoto.SmoothingMode = SmoothingMode.AntiAlias;

            //Draws the photo Image object at original size to the graphics object.
            grPhoto.DrawImage(
                imgPhoto,// Photo Image object
                new Rectangle(0,phWidth,phHeight),// Rectangle structure
                0,// x-coordinate of the portion of the source image to draw. 
                0,// y-coordinate of the portion of the source image to draw. 
                phWidth,// Width of the portion of the source image to draw. 
                phHeight,// Height of the portion of the source image to draw. 
                GraphicsUnit.Pixel);                    // Units of measure 

            //-------------------------------------------------------
            //to maximize the size of the Copyright message we will 
            //test multiple Font sizes to determine the largest posible 
            //font we can use for the width of the Photograph
            //define an array of point sizes you would like to consider as possiblities
            //-------------------------------------------------------
            int[] sizes = new int[] { 25,16,12,10,8,6,4 };

            Font crFont = null;
            SizeF crSize = new SizeF();

            //Loop through the defined sizes checking the length of the Copyright string
            //If its length in pixles is less then the image width choose this Font size.
            for (int i = 0; i < 7; i++)
            {
                //set a Font object to Arial (i)pt,Bold
                crFont = new Font("arial",sizes[i],FontStyle.Bold);
                //Measure the Copyright string in this Font
                crSize = grPhoto.MeasureString("AlexMaslakov.ru",crFont);

                if ((ushort)crSize.Width < (ushort)phWidth)
                    break;
            }

            //Since all photographs will have varying heights,determine a 
            //position 5% from the bottom of the image
            int yPixlesFromBottom = (int)(phHeight * .05);

            //Now that we have a point size use the Copyrights string height 
            //to determine a y-coordinate to draw the string of the photograph
            float yPosFromBottom = ((phHeight - yPixlesFromBottom) - (crSize.Height / 2));

            //Determine its x-coordinate by calculating the center of the width of the image
            float xCenterOfImg = (phWidth / 2);

            //Define the text layout by setting the text alignment to centered
            StringFormat StrFormat = new StringFormat();
            StrFormat.Alignment = StringAlignment.Center;

            //define a Brush which is semi trasparent black (Alpha set to 153)
            SolidBrush semiTransBrush2 = new SolidBrush(Color.FromArgb(153,0));

            //Draw the Copyright string
            //grPhoto.DrawString(Copyright,//string of text
            //    crFont,//font
            //    semiTransBrush2,//Brush
            //    new PointF(xCenterOfImg + 5,yPosFromBottom + 5),//Position
            //    StrFormat);

            //define a Brush which is semi trasparent white (Alpha set to 153)
            SolidBrush semiTransBrush = new SolidBrush(Color.FromArgb(153,255,255));

            //Draw the Copyright string a second time to create a shadow effect
            //Make sure to move this text 1 pixel to the right and down 1 pixel
            grPhoto.DrawString("AlexMaslakov.ru",//string of text
                crFont,//font
                semiTransBrush,//Brush
                new PointF(xCenterOfImg,yPosFromBottom),//Position
                StrFormat);                               //Text alignment



            //------------------------------------------------------------
            //Step #2 - Insert Watermark image
            //------------------------------------------------------------

            //Create a Bitmap based on the previously modified photograph Bitmap
            Bitmap bmWatermark = new Bitmap(bmPhoto);
            bmWatermark.SetResolution(imgPhoto.HorizontalResolution,imgPhoto.VerticalResolution);
            //Load this Bitmap into a new Graphic Object
            Graphics grWatermark = Graphics.FromImage(bmWatermark);

            //To achieve a transulcent watermark we will apply (2) color 
            //manipulations by defineing a ImageAttributes object and 
            //seting (2) of its properties.
            ImageAttributes imageAttributes = new ImageAttributes();

            //The first step in manipulating the watermark image is to replace 
            //the background color with one that is trasparent (Alpha=0,R=0,G=0,B=0)
            //to do this we will use a Colormap and use this to define a RemapTable
            ColorMap colorMap = new ColorMap();

            //My watermark was defined with a background of 100% Green this will
            //be the color we search for and replace with transparency
            colorMap.OldColor = Color.FromArgb(255,0);
            colorMap.NewColor = Color.FromArgb(0,0);

            ColorMap[] remapTable = { colorMap };

            imageAttributes.SetRemapTable(remapTable,ColorAdjustType.Bitmap);

            //The second color manipulation is used to change the opacity of the 
            //watermark.  This is done by applying a 5x5 matrix that contains the 
            //coordinates for the RGBA space.  By setting the 3rd row and 3rd column 
            //to 0.3f we achive a level of opacity
            float[][] colorMatrixElements = { 
                                                new float[] {1.0f,0.0f,0.0f},new float[] {0.0f,1.0f,0.3f,1.0f}};
            ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);

            imageAttributes.SetColorMatrix(wmColorMatrix,ColorMatrixFlag.Default,ColorAdjustType.Bitmap);
            #endregion

            //Replace the original photgraphs bitmap with the new Bitmap
            imgPhoto = bmWatermark;
            grPhoto.Dispose();
            grWatermark.Dispose();
            bmPhoto.Dispose();

            //save new image to file system.
             imgPhoto.Save("copyrighted_"+imageFile,ImageFormat.Jpeg);
            imgPhoto.Dispose();

        }