Accidentally deleted iPhoto and lost all of my photos, how can I get the photos back?
Assuming you didn’t delete your iPhoto Library, but just iPhoto


Reinstall iPhoto from the Mac App Store [you did this, go to 2]
Hold down the option key while opening iPhoto to select a different default library. The current default is the empty library. We want to track down your original library. 
Click “Choose library...”
By default, your iPhoto Library is located in /Volumes/&lt;HDNAME&gt;/Users/&lt;USERNAME&gt;/Pictures/. Assuming you haven’t deleted the library itself, or moved it to a different location, your original iPhoto Library will be located in your pictures folder. It will be labeled iPhoto Library_2.iphotolibrary, iPhoto Library.iphotolibrary~old or something of that nature. I don’t know what the exact name will be. You will be able to tell the new from the old simply by examining the size (800 photos will be atleast a couple GB’s). Select the old library. 
When iPhoto opens, your original library should be present and intact. If it’s not, you’ve just selected the current default library. Repeat steps 2-4 in this case. 
Once you have identified the correct original library - using step 5 - you can now safely delete the empty (false) iPhoto Library from your pictures folder. Your original iPhoto library is now your default.