1) Consider the wisdom of sending a dick picture. If the relationship she is seeking could be construed as a "dating" or "friendly" one, sending your dick at all is mega creepy. And even in the context of casual sex and cybersex, women aren't necessarily aroused by penis JPGs. You might want to wait for her to ask for a dick picture, rather than using it to introduce yourself.
2) Make sure your equipment is suitable. The proper condition for dick photos is clean and dry (seriously, ewww), fully erect, and with well-groomed pubes. If it can stay fully erect without you death-gripping it around the base, so much the better.
(I admit here I don't know exactly how these things work. Is it uncomfortable to let an erect dick flop around freely? Or is the grip necessary to keep it at full hardness? Or does the grip just keep it pointed at a more impressive angle?)
3) Make sure your other equipment is suitable. Take your dick pics with a real camera; a low-end cellphone photo or webcam stillshot always has that "surveillance footage" look to it, especially in low light. Even with a proper camera, all photos look creepy when there isn't enough light (and flash makes skin look unappealingly flat and pallid), so try to get it in as much light as possible. Natural light is really nice if you have a way to get it without scandalizing the neighbors.
4) Use a self-timer or a (clean!) mirror. The top-down perspective never flatters, and frankly, women aren't used to seeing dicks from that angle.
5) Put the penis in context. In my experience, the more of your body in the shot, the better--even if you don't have an amazing body, seeing a naked man is more fun than seeing a free-floating cock in space. Whether you're comfortable putting your face in the photo is up to you, but cropping out everything but genitals is going way too far unless you have a very distinctive lower-stomach tattoo.
6) Don't forget the background. Make sure there isn't weird clutter in the shot that makes you look like a slob or reminds the viewer of an unsexy part of your life. And remember that photos taken while you're in the computer chair, then uploaded onto that selfsame computer, tend to imply that maybe you never get up. Your bed generally makes a nice suggestive setting, if it's tidy.
7) If your camera takes enormous photos, scale it down to something moderate in size so it doesn't display on her monitor as MONITOR FULL OF COCK WHAM. This also hides minor imperfections. And while you've got it in the image-editing program, you might try to get the skin tones to resemble skin--dicks seem prone to photographing in horrible colors like "fishbelly yellow-white" and "roast beef gray-brown," and that's never pretty.
8) Look at the photo you've just taken. Think, seriously, if you were a woman, would you want to see this? Seriously. You can always back out now and tell her about your personality instead.