There is a right way and a wrong way to present using images. The first thing to know is randomly taking images from the internet is not only unprofessional, but in most cases illegal. Most images that you find on the internet are copyright protected and if your presentation is recorded or published online anywhere you could find yourself owing the owner of those images a lot of money. Best advise; don’t do it.
Secondly, most images from he internet are of poor quality and really do not help to make your presentation look professional.
There are many places where you can obtain good quality images, legally, that are free. The best place is Flickr. Flickr has a category called “creative commons” and what this essentially means is that the images are made available by the owner for you to use for non-profit purposes. Non-profit purposes means they cannot be used in product materials where the intention is to sell something, or in a book or magazine article where your direct purpose is to make a profit. However, if you want to use the images in your presentation, then generally this will be OK as long as you make sure that you credit the owner for the image in your presentation.
How To Use Images
Once you have selected your images, just randomly placing the images in your slide is unlikely to have the impact you desire. As will all things design there is a right way and a wrong way to make your point. Let’s look at an example:

In this example, the image has a white background, but the slide has a graduated black to grey background. This is a common error many presenters make. To give this image more impact you could change the background to white and resize the image to fit the slide.
There is also another problem with this image. The main speaker is facing away from the words so your eyes are drawn away from the words. Try to make sure that the main person in the image is facing the words to give them greater impact.

Now the image takes centre stage and the impact of the slide is greater. “a picture paints a thousand words” and it our job as presenters to make those pictures paint those words.
A word of warning here…. If you have a low quality image, then resizing to fit your slide could distort the image and this looks very bad. So when it comes to using images, search for good quality images that will allow for some resizing.
In his blog, Presentation Zen, Garr Reynolds shows some excellent sample slides on other ways you can or cannot use images. Click here to view
Personally, I like images where there is a lot of white space for text. Here is a sample slide where there is plenty of space for text.

In this slide you can see there is a lot of free space on the right side of the image to place some text or words. The slide is not busy, or cluttered and it makes for a nice, clean, calm image.
So, next time you set about creating your presentation, remember, the images you use will make a huge difference to the professionalism of your presentation.