Is your program Photoshop Elements 12 or Premiere Elements 12? If Photoshop Elements, then you have posted in the wrong forum. Some how your thread got posted in the Premiere Elements Forum (video editing).
You could be referring to photos in Photoshop Elements 12 or split screen in Premiere Elements 12/12.1. If Premiere Elements 12/12.1, then please review and consider the information in my blog on Split Screen basics
This applies to Premiere Elements 11, 12/12.1, and 13/13.1.
If you are referring to viewing photos in Photoshop Elements 12, then please re-post your thread in the Adobe Photoshop Elements Forum or wait for a moderator to see your thread here and move it from here to there.
Are your photos the same photo or different ones. Are you looking for a before and after for the same photo? Please give details when re-posting. You might want to look at Elements Organizer 12/12.1, View Menu/Full Screen and, when Full Screen opens, select your two photos, go to View on the pop up options bar and select either the horizontal or vertical pairing.