Ghostscript can do this.

gs -dBATCH -dNOPAUSE -sDEVICE=jpeg -sOutputFile=alllis.jpg -r100 alllis.ps
The resolution is set by the -r#

I actually stick this at the end of the doals script with this line.
gs -dBATCH -dNOPAUSE -sDEVICE=jpeg -sOutputFile=$name.jpg -r100 name.ps

NOTE: -soutputFile used to work, but upon updating my computer I have to use -sOutputFile. So if one doesn't work, try the other one.