Application for calculating ELFO fragment length - (Jan/14/2013 )

There are many manuals how to calculate an exact lenght of DNA elfo fragment using marker and semi-log plot, but I don't kind of feel like actually drawing it

There sure must be a program (app) that can do that from the gel image (even if you need to manualy set the markers and lengths).
Do you know of any (free, Win or online)?
Thanks.

I think ImageJ has a plugin.