Images are drawn with glDrawPixels
glDrawPixels(width, height, format, type, pixels)
width & height are the size of the image, in pixels.
format is GL_RGB for RGB images, or GL_LUMINANCE for greyscale
(there are also several other possible formats).
type indicates the type of one channel of one pixel's data.
Normally GL_UNSIGNED_BYTE, for 8-bit-per-channel images.
pixels is the actual array of image data.