If you have a white rectangle enclosing any of your images, it is because the background is not transparent.  In the PowerPoint example below, it is obvious that the two images on the left do not have transparent backgrounds, and the ones on the right do.  Unless the background color of your presentation is always white, your images will always be enclosed by a white rectangle.  Less than esthetically pleasing....

Here are a few tip's to point you in the right direction if you want to have transparent images in your PowerPoint presentation.  Image formats that can posses transparency are GIF89a, TIF and PNG.  Transparent capability in images is sometimes referred to as 'alpha channel'.  It is beyond the scope of this eNewsletter to describe creating, or editing images to enable transparency.  But, now you will know why that white rectangle is around your images, and have a hint as to how you can correct that situation.

We use Adobe PhotoShop and Adobe Illustrator to create, or edit graphics elements to achieve transparency in bit-mapped, or vector images for screen and print requirements.  There are other programs that will handle these tasks, but these products are used by professionals, and accepted by service bureaus and graphic houses worldwide.  We use these tools, and others to create and edit image libraries for customers, so that their images are in the appropriate format and accessible to anyone needing to create, or edit a presentation.  If you have in-house graphics capability, ask for images with transparency. 

Incorporate images with transparent backgrounds in your next presentation - you will see the difference!