To help identify a plant, photos should obviously be as clear and sharp as possible. The ideal is a close-up of the flower, with a second photo showing the plant with its leaves. Often, the lower leaves are different from those on the flowering stem; it's important to show the lower leaves as well.
As usual with any picture for the forum, it's best to keep the width down to a maximum of about 760 pixels, and the height down to about 555 pixels. If it's much bigger than that, when people click on the thumbnail picture to see it full size, the full size picture will be much bigger than their computer screen, so they will have to scroll around too much to take it in properly.
In the text of your message give as much information as you can about where you saw the plant, if it was growing wild: the type of habitat as well as the location. Size details can also help – height of plant, length and width of leaf and of petals etc.
