A: Sorry - But you can’t increase resolution on something. Don’t let people tell you that you can no matter how much you’d like to believe them. I say that with 15 years of experience working in commercial printing. I also say that because we (Parentfinder and your agency) want you to have an amazing printed profile! :-)
If the information is not there in the image you have, then Photoshop or some other freeware isn’t going to find it and add it in. It just can’t. The result is blur or pixilation seen in this photo of a water lily. The blur is caused by missing information within the photo of the flower. If you’ve got a photo that measures 4” x 6” (physical) and 300dpi - you blow it up to 8x10 - it's going to be less than 300dpi no matter what you try to do to increase it. The opposite however it will work great. So you can take away size and be fine, you just can't add to it. Since the profile we use for printing, eBook and flipbook contains some full page or two page spreads, your cover photo for instance, we need larger photos for those pictures. Again - something that is 72dpi at 7inches will print fine if we are printing postage stamps. Start your original as high as you can (be it a scan or photo) and keep it because that's as large and as good looking as it will ever be.