Error adding graphics to iframe

Trying to add a graph:

<iframe src="" width="450" height="200" frameborder="0"></iframe>

But the error comes out:

Refused to display '' in a frame because it set 'X-Frame-Options' to 'deny'. LINE: 0 IN: LEVEL: ERROR 

I have apache2-server

The actual error is:

it set ‘X-Frame-Options’ to ‘deny’

to overcome this you need to set allow-embedding=true.