Resizing texture


I have the case that I need to resize a jpg to another size, my idea was to try that with opengl and textures.
What would the basic way be? I apply the image as texture to an object. this object should be in screen coords and in the size I need, is this correct? then how can I get the texture back from the gpu back?

you can use glReadPixels to get pixels back from the framebuffer.