Thanks for the tips everyone. Along the way I also stumbled upon Free Sheet Music Links - which Kat first brought to my attention.
The overwhelming majority of sites these days tend to provide a link to the music's digital source be it Midi, ABC or NoteWorthy.
Those that don't typically seem to have low resolution, low contrast or both. The greatest problem from my perspective is the poor contrast, and I've yet to find a package which does a good job increasing contrast without sacrificing resolution.
My best results to date follow the following notional sequence:
Save the target image as a .bmp
Use an imaging package to improve contrast ??
Increase the image size without makung it blurry - I think I have this under control.
Modify the image to be a single colour .bmp. This took me ages to get right. I would be keen see how others might do this as most packages concentrate on colour image effects.
Download the image to SharpEye for notation processing.
Tidy up the file using NWC or Cakewalk.
Is it all worth the effort? My best answer at this stage is "Why not?".
Any further help would be appreciated. Regards, John