first upload the image file to bw system with SE80 - click mime repository,
expand sap-bw-customer-images and right click 'import mime objects'
and choose your file from local pc.
in wad add the image and specify the path
<image src = '../sap/bw/Mime/customer/filename>
hope this helps.
Go to SE80 -> click mime repository -> Expand SAP -> Expand BW -> Expand Customer -> Images.
You'll see a list of images.
Now, right click on Images -> Import MIME Object -> Enter the path and then save.
The folder is not BRAT but it has to be Customer.
Please add the picture to the correct folder and i am sure you'll be able to see the image.