Convert the JPG to BMP format using your favorite image application. Windows Paint will do it, and whatever Linux has standard will do it as well.

Then, you can pull the pixel data directly out of the BMP file. The conversion will most likely produce an image with 24 bits-per-pixel, but you can find that answer in the header info of the BMP file. Also in there is the location of the pixel data. Look up the Wikipedia page for "BMP format". It's simple to understand, just from wiki's image of the format.

If 24-bit, the data will be one byte of blue, one byte of green, one byte of red, etc...to the end of the file. Yes, the data is stored BGR instead of RGB.

That data you now have is RGB888. You can convert it easily enough to RGB565. I have a very recent thread on here (StackOverflow) showing three different conversion algorithms.

Here's my quick attempt. I didn't bother rotating the image. LCD image looks better than my terrible camera allows.