My pictures are being placed in the inappropriate events; like laying on top of other pictures.

Question

HELP  and THANKS    I am in  iPhoto. I have 29,000 pictures.  I have about 1500 events.  I have dragged a very few if these pictures from the internet.  I have dragged one picture from Facebook,  I have received eMails with pictures that I have put in iPhoto library.  I have also brought pictures from the  iPhone into my iPhoto library.
A problem has recently emerged.  Three of the pictures which I have dragged into my iPhoto library have superimposed themselves upon photos which were already in the library.  When I double click on any one of these three recently imported pictures to get an enlarged view of it, the picture that becomes enlarged is not the one that I just double clicked . . .it is a pre-existing photo in my library.  This phenomenon suggests to my mind that that the (recently imported) photo on which I just clicked has somehow superimposed itself over the pre-existing photo.  ?????   What a strange dilemma!   HELP.
This is the problem and a recent problem.  I have three separate pictures that I have brought into the library that are causing a problem. One is from the Facebook, one is from an eMail, one is from a library file that I bought online. They have perpetuated, that is they have placed themselves on top of other pictures in many events.  The said pictures can be seen  and have been renamed the file into which they are going and going and going.  When I click on the said pictures up comes the original picture that has the event name.  I have tried to trash the picture and bring back the pictures only to find the returning problem.  Please someone please help.  The problem is that one picture is superimposed upon another picture.
I took my computer to SimplyMac and they reloaded the thumbnails and said that would fix the probable. It didn't!  Now what! 
Thanks again!

Answer 1

If Larry's suggestion doesn't help the situation Try the following:
1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your
     User/Home/Library/ Preferences folder.
2 - delete iPhoto's cache file, Cache.db, that is located in your
User/Home/Library/Caches/com.apple.iPhoto folder (Snow Leopard and Earlier).
or with Lion, Mt. Lion or Mavericks delete the contents the User/Library/Containers/com.apple.iPhoto/
Data/Library/Caches/com.apple.iPhoto folder.
3 - reboot, launch iPhoto and try again.
NOTE: In Lion and Mountain Lion the Home/Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and press the Return key - 10.7: Un-hide the User Library folder.
If you're running Mavericks, 10.9,  go to your Home folder and use the View ➙ Show View Options menu to bring the this window:
where you can check the Show Library Folder checkbox.
OT