While building PDF with DITA-OT, fop fails to find image

[Kk Mm]

Dear all

Thank you in advance and please forgive me I'm so new to Linux and DIta.

On CentOS7 (on Azure), I'm trying to build a PDF with DITA-OT 3.3.3, but FOP cannot find images.

In local CentOS7 (on VirtualBox), everything was all right.

But when I moved all to CentOS7(on Azure), the error blow comes up and PDF is rendered without any image.

[fop] [ERROR] Image not found. URI: http://xx.xx.xx.xx/public/blog_images/01-fullsize.png. (See position 10:144)

[fop] [ERROR] Image not found. URI: http://xx.xx.xx.xx/public/blog_images/04-fullsize.png. (See position 25:144)

[fop] [ERROR] Image not found. URI: http://xx.xx.xx.xx/public/blog_images/02-fullsize.png. (See position 52:143)

[fop] [ERROR] Image not found. URI: http://xx.xx.xx.xx/public/blog_images/03-fullsize.png. (See position 60:144)

when I copy & paste the URI on the browser, I can access to the image., 

also the permission for the blog_images folder is "drwxr-sr-x", and the images are "-rwxr-xr-x apache:apache".

Could any one guide me where and what I'm doing wrong?

Thank you