You need to read the chapter in the PCL5 Technical Reference manual on raster graphics. I'm sure that Chris H. can give you a pointer to the pdf file. He is VERY organized. This is a huge topic and is not something that will be answered in a forum message.
My MKPCL program only supports BMP, JPG, and PCX raster file formats. You can go to the website a get a demo if you want.
Consider that the PCL sequences are simply sending the raster data one row at a time top to bottom to the printer. This means that you must first decode and extract the raster data from the image file and then add the PCL instructions. The image file formats are of course all different.
Printing in color vs. BW changes the game as well. Chris H. referenced this in his mention of the Configure Image Data sequences. If you need to support color printing, then you will need to see the PCL 5 Color Reference.