How can you create a uniform appearance by adding a background image to all slides?

Go to Design>Background Styles>Fill>Select picture and texture fill>insert file>click ok

*above steps are for office2010

in ms power point 1st of all we go to design ribbon then click option on background style then format option click on fill then click on picture and texture option then click on file and choose ur file that u want . we can also use gradient option for background colors dark and light.