When create a PPT choosing the proper image is very important, the "appropriate" absolutely does not mean the more beautiful the better, the larger the better, sometimes we need to deliberately ignore texture and beauty of an image under particular circumstance. The key point is to select the specific that match the whole rhythm and background the PPT needs to be. The following is my personal experience to share with you.
The larger images often taken with high resolution, which is more clear, quality and can be transformed freely to meet users' requirements. On the other hand, when display under full screen mode, they will have better visual impact to match text or other element. If you only have low resolution images, I suggest do not use them.
Choose the picture that match with the PPT style and color, which will provide consistent results. A randomly selected image may cause an abrupt impression. Therefore, in the production of PPT, strategy is very important. Good photos often highlight your work.