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If its not on opencores, then it's not likely to be free.
Jpeg decoding isn't something you usually need on fpga, as a single image isn't exactly a lot of data. Fpgas address much better at stream processing.
The Xilinx code you've found might be portable to altera. Otherwise you'll have to write your own core.
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I am sorry I did not make it clear that I am using the camera at video mode. So, in fact, I have a stream of jpeg images (30 fps) that I need to decode. My advisor suggested me to move the jpeg decoder to vhdl, which I have problems with. Thank you for your response.