My popup images do not overlap my YouTube video.

At the time of writing, YouTube's embed code is included within an iframe. If your pop up images are displaying behind the YouTube video then making the following alteration to the YouTube embed code will resolve the problem. 

• Having inserted a YouTube video into your web page document, select the YouTube video and go to Web Properties > Placeholder tab.
• Select the HTML code (body) button.  This will cause the code for the YouTube video to display.
• The code will look similar to below
• <iframe width="425" height="349" src="http://www.youtube.com/embed/vylCpEAEJ7o" frameborder="0">&lt;/pre&gt;&lt;/li&gt;&lt;/ul&gt;&lt;/div&gt;</iframe>
• Within the code, the value of src causes your chosen video to load 
• change the placeholder code to read
  
  <iframe width="425" height="349" src="http://www.youtube.com/embed/vylCpEAEJ7o?wmode=transparent" frameborder="0">&lt;/pre&gt;&lt;/li&gt;&lt;/ul&gt;&lt;/div&gt;</iframe>
• Adding wmode=transparent will allow your popup images to overlap the YouTube video.
• Select the OK button followed by the Apply button to apply the changes.