for ur first question, first go into surface editor->then select which surface u want glowing->click on advanced tab and change the glow intensity to 100%->close surface editor and click on Scene tab->click on image processing under the effects menu->check enable glow in the image processing window and then render away.
f u wanna change any settings of the glow, just change the options in the image processing window beside glow.
Question 2
well, the picture will stretch if its smaller than size of screen or camera resolution. u could change the camera resolution settings in the camera properties and see if ur picture fits in as the background without any stretching...
I hope that answered both ur questions...