Using an image as the background of a slide can add a lot of interest, but can have negative effects on an audience’s ability to read the words. The example slide below shows how “text glow” shadows can make it easier to read.
The title uses no glow, the 1st bullet uses a 1 pixel border, and the 2nd and 3rd bullet points use progressively more aggressive border styles.
In a Mac, you can add this by selecting the text, and going to the Format menu, and selecting the Font option.
Then, choose the”Text Glow & Soft Edges” option. From here, you can set the color, thickness, and transparency. A high transparency value increases the background bleeding through the glow.
In a PC, right-click on text, and choose “Format Text Effects.”
Then, in the following menu,go to “Glow and Soft Edges” and add a color, size, and set the transparency.
While it takes a little hunting to find the option, this option can greatly enhance the legibility of text on top of a complex image.