Saveimg will work in paperspace and capture everything, but it also captures what is outside your layout. What you will want to do is zoom extents your layout, then pan your paper all the way to the left. Then after entering saveimg at the command line, play with the "size" of your "x" in the "Save Image" dialog box. By doing this, it will crop wherever your inputs are. For example, for an 8 1/2 x 11 size sheet, I entered "400" in the "x" input box and it only saved the sheet, not the background of paperspace. By using zoom extents, and trial + error, you will find the best inputs for cropping. If you didn't use zoom extents, you would also have to play with your "Y" value.
By the way, for whatever reason, a .bmp file format captured everything, but saving the exact same things in a .tiff I lost my text.
Flores