In a PowerPoint presentation or Web page, the transparent area will have the color of the background. On the Standard toolbar, click Set Transparent Color . Position the tool over the color you want to make transparent, and click. The Change Color to Transparent dialog box appears. You can modify the options to increase the range of colors that will become transparent or to change the degree of transparency.
Transparency is saved in different ways by different graphics file formats.
GIF saves all transparency values by substituting a transparent color in place of the designated color. If you are concerned about loss of image data, use TIFF or PNG to save your image. In 24-bit images, TIFF saves transparency in an alpha channel. For monochrome and 8-bit TIFF images, however, Photo Editor does not save transparency. In 24-bit images, PNG saves transparency in an alpha channel.