在指定图片上生成文字，文字格式可调，最终效果为

public class Waterark
{
private int _width;
private int _height;
private string _fontFamily;
private int _fontSize;
private bool _adaptable;
private FontStyle _fontStyle;
private bool _shadow;
private string _backgroundImage;
private Color _bgColor;
private int _left;
private string _resultImage;
private string _text;
private int _top;
private int _alpha;
private int _red;
private int _green;
private int _blue;
private long _quality;

public Waterark()
{
//
// TODO: Add constrUCtor logic here
//
_width = 460;
_height = 330;
_fontFamily = "方正喵呜体";
_fontSize = 28;
_fontStyle = FontStyle.Regular;
_adaptable = true;
_shadow = false;
_left = 45;
_top = 80;
_alpha = 255;
_red = 250;
_green = 250;
_blue = 250;
_backgroundImage = "";
_quality = 100;
_bgColor = Color.FromArgb(255, 229, 229, 229);
_shadow = false;

}

/**/
/// <summary>
/// 字体
/// </summary>
public string FontFamily
{
set { this._fontFamily = value; }
}

/**/
/// <summary>
/// 文字大小
/// </summary>
public int FontSize
{
set { this._fontSize = value; }
}

/**/
/// <summary>
/// 文字风格
/// </summary>
public FontStyle FontStyle
{
get { return _fontStyle; }
set { _fontStyle = value; }
}

/**/
/// <summary>
/// 透明度0-255,255表示不透明
/// </summary>
public int Alpha
{
get { return _alpha; }
set { _alpha = value; }
}

/**/
/// <summary>
/// 水印文字是否使用阴影
/// </summary>
public bool Shadow
{
get { return _shadow; }
set { _shadow = value; }
}

public int Red
{
get { return _red; }
set { _red = value; }
}

public int Green
{
get { return _green; }
set { _green = value; }
}

public int Blue
{
get { return _blue; }
set { _blue = value; }
}

/**/
/// <summary>
/// 底图
/// </summary>
public string BackgroundImage
{
set { this._backgroundImage = value; }
}

/**/
/// <summary>
/// 水印文字的左边距
/// </summary>
public int Left
{
set { this._left = value; }
}

/**/
/// <summary>
/// 水印文字的顶边距
/// </summary>
public int Top
{
set { this._top = value; }
}

/**/
/// <summary>
/// 生成后的图片
/// </summary>
public string ResultImage
{
set { this._resultImage = value; }
}

/**/
/// <summary>
/// 水印文本
/// </summary>
public string Text
{
set { this._text = value; }
}

/**/
/// <summary>
/// 生成图片的宽度
/// </summary>
public int Width
{
get { return _width; }
set { _width = value; }
}

/**/
/// <summary>
/// 生成图片的高度
/// </summary>
public int Height
{
get { return _height; }
set { _height = value; }
}

/**/
/// <summary>
/// 若文字太大，是否根据背景图来调整文字大小，默认为适应
/// </summary>
public bool Adaptable
{
get { return _adaptable; }
set { _adaptable = value; }
}

public Color BgColor
{
get { return _bgColor; }
set { _bgColor = value; }
}

/**/
/// <summary>
/// 输出图片质量，质量范围0-100,类型为long
/// </summary>
public long Quality
{
get { return _quality; }
set { _quality = value; }
}

/// <summary>
/// 立即生成水印效果图
/// </summary>
/// <returns>生成成功返回true,否则返回false</returns>
public bool Create()
{
try
{
Bitmap bitmap;
Graphics g;

//使用纯背景色
if (this._backgroundImage.Trim() == "")
{
bitmap = new Bitmap(this._width, this._height, PixelFormat.Format64bppArgb);
g = Graphics.FromImage(bitmap);
g.Clear(this._bgColor);
}
else
{
bitmap = new Bitmap(Image.FromFile(this._backgroundImage));
g = Graphics.FromImage(bitmap);

}
g.SmoothingMode = SmoothingMode.HighQuality;
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.CompositingQuality = CompositingQuality.HighQuality;

Font f = new Font(_fontFamily, _fontSize, _fontStyle);
SizeF size = g.MeasureString(_text, f);

// 调整文字大小直到能适应图片尺寸
while (_adaptable == true && size.Width > bitmap.Width)
{
_fontSize--;
f = new Font(_fontFamily, _fontSize, _fontStyle);
size = g.MeasureString(_text, f);
}

Brush b = new SolidBrush(Color.FromArgb(_alpha, _red, _green, _blue));
StringFormat StrFormat = new StringFormat();
StrFormat.Alignment = StringAlignment.Near;
if (this._shadow)
{
Brush b2 = new SolidBrush(Color.FromArgb(90, 0, 0, 0));
g.DrawString(_text, f, b2, _left + 2, _top + 1);
}
//g.DrawString(_text, f, b, new PointF(_left, _top), StrFormat);

if (_text.Length <= 4)
{
g.DrawString(_text, f, b, new PointF(140, 150), StrFormat);
}
else if (4 < _text.Length && _text.Length <= 8)
{
g.DrawString(_text, f, b, new PointF(90, 150), StrFormat);
}
else if (8 < _text.Length && _text.Length <= 11)
{
g.DrawString(_text.Substring(0,4), f, b, new PointF(140, 110), StrFormat);
g.DrawString(_text.Substring(4, _text.Length-4), f, b, new PointF(90, 150), StrFormat);
}
else if (11 < _text.Length && _text.Length <= 18)
{
if (_text.Length % 2 == 1)
{
g.DrawString(_text.Substring(0, (_text.Length-1)/2), f, b, new PointF(60, 110), StrFormat);
g.DrawString(_text.Substring((_text.Length - 1) / 2, _text.Length - (_text.Length - 1) / 2), f, b, new PointF(60, 150), StrFormat);
}
else
{
g.DrawString(_text.Substring(0, (_text.Length - 1) / 2), f, b, new PointF(60, 110), StrFormat);
g.DrawString(_text.Substring((_text.Length - 1) / 2, _text.Length - (_text.Length - 1) / 2), f, b, new PointF(60, 150), StrFormat);
}

}
else if (18 < _text.Length && _text.Length <= 25)
{
g.DrawString(_text.Substring(0,8), f, b, new PointF(60, 110), StrFormat);
g.DrawString(_text.Substring(8,9), f, b, new PointF(45, 150), StrFormat);
g.DrawString(_text.Substring(17, _text.Length-17), f, b, new PointF(60, 190), StrFormat);
}
else if (25 < _text.Length && _text.Length <= 31)
{
g.DrawString(_text.Substring(0, 6), f, b, new PointF(90, 70), StrFormat);
g.DrawString(_text.Substring(6, 8), f, b, new PointF(60, 110), StrFormat);
g.DrawString(_text.Substring(14, 9), f, b, new PointF(45, 150), StrFormat);
g.DrawString(_text.Substring(23, _text.Length - 23), f, b, new PointF(60, 190), StrFormat);
}
else if (31 < _text.Length && _text.Length <= 37)
{
g.DrawString(_text.Substring(0, 6), f, b, new PointF(90, 70), StrFormat);
g.DrawString(_text.Substring(6, 8), f, b, new PointF(60, 110), StrFormat);
g.DrawString(_text.Substring(14, 9), f, b, new PointF(45, 150), StrFormat);
g.DrawString(_text.Substring(23, 8), f, b, new PointF(60, 190), StrFormat);
g.DrawString(_text.Substring(31, _text.Length-31), f, b, new PointF(90, 230), StrFormat);
}
else if (37 < _text.Length )
{
g.DrawString(_text.Substring(0, 6), f, b, new PointF(90, 70), StrFormat);
g.DrawString(_text.Substring(6, 8), f, b, new PointF(60, 110), StrFormat);
g.DrawString(_text.Substring(14, 9), f, b, new PointF(45, 150), StrFormat);
g.DrawString(_text.Substring(23, 8), f, b, new PointF(60, 190), StrFormat);
g.DrawString(_text.Substring(31, _text.Length - 31), f, b, new PointF(90, 230), StrFormat);
}
bitmap.Save(this._resultImage, ImageFormat.Png);

bitmap.Dispose();
g.Dispose();
return true;
}
catch
{
return false;
}
}
}

在指定图片上生成文字，文字格式可调