Sounds like you are concerned about sizing the pic large enough to fir a large format banner. Nobody can help you without knowing the specific size of the pic as it is now. Hopefully it is not an overly compressed JPEG. The quality depends on how well the photograph was originated ( i.e., sharpness, grain, lighting, and overall detail ). Some digital cameras shoot very large RAW files which can then be enlarged without too much trouble. Large format digital printers only require around 120ppi @ 100% final size. You could even get away with 72-100ppi. Again, it all depends on the file size you have. Let us know.