Hi Jihyun,

I am really sorry for the delay of this reply.

Initially you can turn off placeholder image from your backend > easyblog > settings > layout > post options > show image placeholder set to off, http://screencast.com/t/5FTG7ynsOMq . You might also want to take a look on your backend > easyblog > settings > layout > post cover and tick the following check box as you can see from my screenshot here, http://screencast.com/t/piy62kNqZd so that all image will be displayed in full width rather than original width like the picture attachment included in your inquiry.

Hope these help.