First thing I'd do is move the referrence image from the Camera and onto a geometry plane. Much more flexibility, it's leaner/faster and it instantly solves your problem. You can put them on layers and control their behaviour as well. Make them non-clickable etc
Secondly Maya and .jpg images doesn't work so good. When using referrence I always use .tga
When working with .tga you can save them as 32bit alpha channel images yeah. Maya works like this: White is opaque and black is transparent. You must know this for the masking (I always forget to Invert them hah)
Let's say your ref image is: 600px wide and 400px height, create a polygon plane with the dimensions 6.0, 4.0, load your referrence image onto a material and assign the material to this plane.
If none of this made any sense whatsoever. There's a free video tutorial that explains all of this indepth:
Click Tutorials -> Modelling and look for Image plane setup.