Well, you can generate a DDR SDRAM controller in several ways
* go to Micron's website and download the datasheet for a DDR SDRAM memory of the size you require. The datasheets are very complete and have flowcharts and timing diagrams documenting all the procedures required to write, read and maintain data in the memory. You can use these to write your own DDR SDRAM controller. This would teach you the most about how the DDR SDRAM works, and would be very valuable but it would be the most work.
* go to opencores.org and get a DDR_SDRAM controller that'a already written and use that. It may have little or no documentation and it may or may not be error-free. But you'd have code quite quickly.
* Get the mig007 program that I told you about earlier in this thread and generate a DDR SDRAM interface
After you get your interface, you'll have to decide how to get the file from your computer. I do not know which board you have or intend to design, but RS-232 and USB are two common ways of sending data to and from your FPGA. You'll have to determine which methods you have available and which will fit your specification regarding transfer time, etc.
Thirdly, you will have to write RTL that takes data from the FPGA-PC interface and passes it to the DDR SDRAM controller you have instantiated. You will have to determine what, if any, processing you must do to the image data and write the necessary RTL code for that. If all you want to do is store a still image, then just write the bytes into the memory sequentially and read them sequentially. Or use whatever format you wish.
r.b.