防病毒软件会阻止安装程序运行(Antivirus prevents setup program from running)

 根据sunil-antony的回答，我想出了以下解决方案（使用save_graphics_state来附上绘图说明，请参阅Prawn文档）： 
 
Prawn::Document.generate("x.pdf") do 
  image_width = 200
  image_x = 100
  image_y = 100 

  save_graphics_state do
    soft_mask do 
      fill_color 0,0,0,0 
      fill_circle [image_x + image_width/2, image_y - image_width/2], image_width/2
    end 

    image "example.jpg", at: [image_x, image_y], width: image_width, height: image_width
  end
end 

Based on sunil-antony's answer, I came up with the following solution (using save_graphics_state to enclose drawing instructions, see Prawn documentation):
 
Prawn::Document.generate("x.pdf") do 
  image_width = 200
  image_x = 100
  image_y = 100 

  save_graphics_state do
    soft_mask do 
      fill_color 0,0,0,0 
      fill_circle [image_x + image_width/2, image_y - image_width/2], image_width/2
    end 

    image "example.jpg", at: [image_x, image_y], width: image_width, height: image_width
  end
end