PowerPoint offers some powerful graphics-editing capabilities. For example, if you have a clip art picture that you could use a portion of, all you have to do is separate what you want from what you don't, and get rid of the portion you don't want. For example, let's say you want to keep only the dog portion of the Veterinary Medicine picture in the Animals category.
First, insert the picture in your slide by clicking the Insert Clip Art button on the Drawing toolbar or by pulling down the Insert menu, pointing at Picture, and choosing Clip Art. Select the category, click the picture, and choose Insert Clip. Back on the slide, right-click the picture, choose Grouping, and select Ungroup. Answer Yes to verify that you want to convert the picture to PowerPoint objects.
Next, click somewhere on the slide away from the picture to deselect every object, then click on an individual object you'd like to get rid of and press Delete. Continue this process until all the unwanted parts have been deleted. Finally, select the remaining parts of the picture, right-click, choose Grouping, and select Group. Doing so will make the remaining picture act as a single unit.