Getting pictures into PowerPoint and having them look good can sometimes be challenging. Here are some tips to get the best results:
Prepare your pictures before you use them in PowerPoint. If you have good photo-manipulation software such as Photoshop or Paint Shop Pro, touch up and size and crop your pictures there first. They will look their best that way.
If your presentation contains a lot of pictures, the presentation's file size can get very large. Use the Compress Pictures button on the Pictures toolbar to make them smaller.
For better control over your pictures' file sizes, save the picture using the least number of colors possible. You can tell you've saved the picture using too few colors when it starts to look blotchy or grainy.