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In most such cases, the creator of the announcement probably used a very low resolution. For the best possible image reproduction, it is essential that you use the highest appropriate resolution whether you are taking the picture or scanning it into your computer's image editing program. You certainly don't want to use too high a resolution as that will take up too much disk space unnecessarily and may even slow down your computer. For photo birth announcements printed on a home printer, you should be able to get good results with a 250 to 300 dpi resolution. The type of paper that you will use bears some consideration as well.