在你的Dll中：
public class mydll
{
public mydll()
{
this.GetType().Assembly.GetManifestResourceStream( "yourDllName.yourImage.JPG" );
}
public System.IO.Stream ReturnStream()
{
return this.GetType().Assembly.GetManifestResourceStream( "yourDllName.yourImage.JPG" );
}
}
注意要将图片yourImage.JPG 修改"生成方式"(Build Action)为"嵌入资源"(Embeded Resource)
然后在要调用的程序中：
private void Form1_Load(object sender, System.EventArgs e)
{
yourDllName.mydll yy= new mydll();
pictureBox1.Image = Image.FromStream( yy.ReturnStream() );
}