My place to talk about birth announcements
In most such cases, the creator of the announcement probably used a very low resolution. It is important to take pictures or scan them at a sufficient resolution that allows for maximum clarity. That being said, using a too high resolution isn't necessarily the best way to go either, as overly high resolution pictures can eat up too much of your computer's resources and possibly even cause it to grind to a halt. In general, setting your camera or scanner to capture at 250 dpi to 300 dpi should be enough to get you great looking results in a typical consumer printer. The type of paper that you will use bears some consideration as well.