Retrieving old photos from external hard drive without replacing current library

Question

Hi everyone,
This problem has probably been discussed before but I have not been able to find a definitive answer.  Hopefully I can find a solution to this problem here.
I am having trouble with my workflow in iPhoto.  Right now when I place an SD card full of digital photos into my Macbook Pro, I import all of them directly into iPhoto.  I use iPhoto to organize my photos and do simple edits and changes.  However, recently I have begun to fill up my 250GB hard drive with photos and HD video, so I use an external hard drive to backup my computer before deleting unneeded items.  Obviously, the purpose of backing up is to be able to go back and retrieve those items.  With items saved in Documents>Photos, they can be easily organized, and then retrieved later from whatever date they were saved on the external drive, adding them back to the existing photos currently on my computer.  However, iPhoto is a great tool, so I prefer to use it instead.  But I notice that saving an iPhoto library onto a backup drive is not the same as saving a folder full of pictures.  When I try to open an iPhoto library from my external hard drive, it tells me something about not being able to open it, or replacing my current library with the old one just to view my pictures.  I simply want to find old photos saved within iPhoto, and add them to my existing library.  Does iPhoto really only allow you to open one library at a time, and not browse them and add them together?  If so, then just saving photos outside of iPhoto in Documents seems like a better workflow for retrieval, but at the cost of not being able to utilize iPhoto's capabilities.
If my view of how iPhoto works here is very wrong, please let me know.  I just don't want to have to save my photos outside of iPhoto just to be able to find them again without replacing my current photos.  Thanks everyone for your help. 

Answer 1

iPhoto can only open one library at a time.
Here's one way to do what you want:
1. Quit iPhoto.
2. Copy the iPhoto Library from your Pictures Folder to the external drive.
Now you have two full copies of the Library. To choose between them:  Hold down the option (or alt) key and launch iPhoto. From the resulting menu select 'Choose Library'
3. On the Internal Library, remove the pics you don't want with you all the time.
Now you have one full library on the external and another smaller sub-set on the Internal.
A couple of comments:
a. The external disk needs to be formatted Mac OS Extended (Journaled)
b: When you're removing the unwanted pics from the Internal Library you need to delete them in batches of about 100 or so. Trashing more at one time can cause problems with the database.
c: Managing Multiple Libraries - including moving pics/albums/rolls and metadata between them - is greatly facilitated by using iPhoto Library Manager