It is required to redraw both texture and line for every frame.
Gl.glDisable(Gl.GL_LINE_STIPPLE)
img.imgFile = "D:\\Desert.jpg"
img.generateTexture()
Is texture loading necessary for each mouse movement ?
Normally redrawing a texture and line won't create slow rendering.
If any processing which is not related to the mouse movement, and takes much time, then we can use an intermediate texture to hold the output of heavy task. For every frame we can draw that texture with line drawing.