原因是：Unable to load shared library 'gdiplus'
但是即使安装上了这个dll，依然不能显示图片，为啥呢？
.NET Core 2.2 本身依然不包括和图片有关的 Image、Bitmap 等类型。
所以当处理图片的类中使用了ZKWeb.System.Drawing，就会提示：
Connection id "0HLPLMNTFQ8H5", Request id "0HLPLMNTFQ8H5:00000001": An unhandled exception was thrown by the application.
System.ArgumentException: No codec available for format:b96b3cae-0728-11d3-9d7b-0000f81ef32e
at System.DrawingCore.Image.Save(Stream stream, ImageFormat format)
为此百度好久，终于发现链接的文章。
此时如果你用了我的类库则只需切换到System.Drawing.Common库中并安装
sudo curl https://raw.githubusercontent.com/stulzq/awesome-dotnetcore-image/master/install/centos7.sh|sh
或者切换为ImageSharp，就可以避免此问题。
附带图片验证码helper类 使用System.Drawing.Common库
using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
public sealed class VerifyCodeHelper
{
#region 单例模式
//创建私有化静态obj锁
private static readonly object _ObjLock = new object();
//创建私有静态字段，接收类的实例化对象
private static VerifyCodeHelper _VerifyCodeHelper = null;
//构造函数私有化
private VerifyCodeHelper() { }
//创建单利对象资源并返回
public static VerifyCodeHelper GetSingleObj()
{
if (_VerifyCodeHelper == null)
{
lock (_ObjLock)
{
if (_VerifyCodeHelper == null)
_VerifyCodeHelper = new VerifyCodeHelper();
}
}
return _VerifyCodeHelper;
}
#endregion
public enum VerifyCodeType { NumberVerifyCode, AbcVerifyCode, MixVerifyCode };
#region 数字验证码
///
/// 1.数字验证码
///
///
///
/// 2.字母验证码
///
/// 字符长度
/// 验证码字符
private string CreateAbcVerifyCode(int length)
{
char[] verification = new char[length];
char[] dictionary = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'm', 'n', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
};
Random random = new Random();
for (int i = 0; i < length; i++)
{
verification[i] = dictionary[random.Next(dictionary.Length - 1)];
}
return new string(verification);
}
#endregion
#region 混合验证码
///
/// 3.混合验证码
///
/// 字符长度
/// 验证码字符
private string CreateMixVerifyCode(int length)
{
char[] verification = new char[length];
char[] dictionary = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'2', '3', '4', '5', '6', '7', '8', '9',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n','p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
};
Random random = new Random();
for (int i = 0; i < length; i++)
{
verification[i] = dictionary[random.Next(dictionary.Length - 1)];
}
return new string(verification);
}
#endregion
#region 产生验证码（随机产生4-6位）
///
/// 产生验证码（随机产生4-6位）
///
/// 验证码类型：数字，字符，符合
///
/// 验证码图片 => Bitmap
///
/// 验证码
/// 宽
/// 高
/// Bitmap
public Bitmap CreateBitmapByImgVerifyCode(string verifyCode, int width, int height)
{
Font font = new Font("Arial", 14, (FontStyle.Bold | FontStyle.Italic));
Brush brush;
Bitmap bitmap = new Bitmap(width, height);
Graphics g = Graphics.FromImage(bitmap);
SizeF totalSizeF = g.MeasureString(verifyCode, font);
SizeF curCharSizeF;
PointF startPointF = new PointF(0, (height - totalSizeF.Height) / 2);
Random random = new Random(); //随机数产生器
g.Clear(Color.White); //清空图片背景色
for (int i = 0; i < verifyCode.Length; i++)
{
brush = new LinearGradientBrush(new Point(0, 0), new Point(1, 1), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)));
g.DrawString(verifyCode[i].ToString(), font, brush, startPointF);
curCharSizeF = g.MeasureString(verifyCode[i].ToString(), font);
startPointF.X += curCharSizeF.Width;
}
//画图片的干扰线
for (int i = 0; i < 10; i++)
{
int x1 = random.Next(bitmap.Width);
int x2 = random.Next(bitmap.Width);
int y1 = random.Next(bitmap.Height);
int y2 = random.Next(bitmap.Height);
g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
}
//画图片的前景干扰点
for (int i = 0; i < 100; i++)
{
int x = random.Next(bitmap.Width);
int y = random.Next(bitmap.Height);
bitmap.SetPixel(x, y, Color.FromArgb(random.Next()));
}
g.DrawRectangle(new Pen(Color.Silver), 0, 0, bitmap.Width - 1, bitmap.Height - 1); //画图片的边框线
g.Dispose();
return bitmap;
}
///
/// 验证码图片 => byte[]
///
/// 验证码
/// 宽
/// 高
/// byte[]
public byte[] CreateByteByImgVerifyCode(string verifyCode, int width, int height)
{
Font font = new Font("Arial", 14, (FontStyle.Bold | FontStyle.Italic));
Brush brush;
Bitmap bitmap = new Bitmap(width, height);
Graphics g = Graphics.FromImage(bitmap);
SizeF totalSizeF = g.MeasureString(verifyCode, font);
SizeF curCharSizeF;
PointF startPointF = new PointF(0, (height - totalSizeF.Height) / 2);
Random random = new Random(); //随机数产生器
g.Clear(Color.White); //清空图片背景色
for (int i = 0; i < verifyCode.Length; i++)
{
brush = new LinearGradientBrush(new Point(0, 0), new Point(1, 1), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)), Color.FromArgb(random.Next(255), random.Next(255), random.Next(255)));
g.DrawString(verifyCode[i].ToString(), font, brush, startPointF);
curCharSizeF = g.MeasureString(verifyCode[i].ToString(), font);
startPointF.X += curCharSizeF.Width;
}
//画图片的干扰线
for (int i = 0; i < 10; i++)
{
int x1 = random.Next(bitmap.Width);
int x2 = random.Next(bitmap.Width);
int y1 = random.Next(bitmap.Height);
int y2 = random.Next(bitmap.Height);
g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
}
//画图片的前景干扰点
for (int i = 0; i < 100; i++)
{
int x = random.Next(bitmap.Width);
int y = random.Next(bitmap.Height);
bitmap.SetPixel(x, y, Color.FromArgb(random.Next()));
}
g.DrawRectangle(new Pen(Color.Silver), 0, 0, bitmap.Width - 1, bitmap.Height - 1); //画图片的边框线
g.Dispose();
//保存图片数据
MemoryStream stream = new MemoryStream();
bitmap.Save(stream, ImageFormat.Jpeg);
//输出图片流
return stream.ToArray();
}
#endregion
}
附带前端调用
string code = VerifyCodeHelper.GetSingleObj().CreateVerifyCode(VerifyCodeHelper.VerifyCodeType.NumberVerifyCode); byte[] codeImage = VerifyCodeHelper.GetSingleObj().CreateByteByImgVerifyCode(code, 100, 40);
原文： https://www.cnblogs.com/stulzq/p/10172550.html