You can work from photographs you already have of yourself, but taking the actually pictures is an interesting process in itself. You do not have to be a photographer to go about it, just some quiet time and some determination.
A digital camera works best, especially if you have a timer on it.
Don’t be too fussy about lighting, or angles, or backgrounds. These are images that will be used for drawing purposes, not for the cover of a fashion magazine!
By using the timer and placing the camera a few feet away on a shelf, a chair or table, or even the floor, you can photograph your face, your feet, your breasts or your entire body, clothed or unclothed, whatever you want most want or need to work on. You will likely get more adventuresome if you come back to it occasionally over a period of time. If you’re really doing this just for you, I can assure you that with practice the resistance and the judgement make way for new perspectives. The only reason I can testify to this is that not only was how I looked like an absolute obsession for me, I’m also about as prude as they come.
If you share a computer and don’t want other people seeing your photos, remember you can always save them to a USB key, or, have your own memory card for the camera that can be taken out when you’re finished.
Just let loose and experiment, sometimes the mistakes are as interesting as the well-framed images!