Raster File Editors

Hi guys, can anyone recommend a good raster file editor.?

I have been approached to provide Drawing Office Support Services for a local company, all their drawings are Autocad format or scanned files (tiff G4 format). As there appears to be nothing that works with Intellicad I need a stand alone package. Until now I've got by, but if I get the contract I must pass a software audit!!!!

Any suggestions please.