You mean getting an image into the webpage ?
Try first to load the webpage from the SD card.
There are examples for that.
Adding pictures is simple after that.
The browser sends a 'GET' request for the image, and you return it with the proper content type header.
The content type for html is "text/html" and for a *.jpg file it is "image/jpeg".
If you expand that for all types, you can have a whole site with subdirectories, javascript and stylesheets on the SD card.
I have my webpage on the SD card, and use the text "$1" and "$2" in the webpage where the Arduino will place its own data.
So while loading the webpage from the SD card, I check for '$' and read the number after it.