You have a 5-megapixel main camera. I believe taking a picture of the receipt with it should be sufficient for any MSC. I use a 5 MP phone and have never had an issue. I also have a scanner at home, but mostly just take pictures since I find it is quicker.
Some MSCs will require you to shrink the file size. Marketforce used to have a 1 MB limit on their old website.
Also, a scanning program would probably just allow you to save the scan as a .pdf instead of a .jpg, but most want a .jpg file uploaded.
It would use the camera to scan the receipt, so why use another program on your phone?