PaulS:
You need, as sterretje points out, to actually look at what the client is requesting, and supply the appropriate response, which MIGHT be nothing, as the client is also likely to request favicon.ico, which you do not need to respond to.
OP:
You haven't seemed to let this advise soak in. I don't see any place in your code where you're looking at the request from the client and responding appropriately. Wait for the request for the image to come in, then open the file on the SD card and stream it to the client in response. Then, close the file.