I have a friend who recently upgraded his very old iMac to Yosemite.  He then realized that he could not find his old iPhoto images.  He had made a number of mistakes which I list next:

• He did not back up his hard drive prior to this major system upgrade.
• He did not use Time Machine.
• He did not have an iCloud backup solution
• He did not have an external hard drive or USB finger drive copy of his photo images.

We checked the Internet for a solution but we could not find one.  It seems that with the recent software system upgrade, Apple changed iPhoto Library.  I was able to find the images for him using this method.

NOTE: This method might not work for you.  Proceed with caution.

Please note that the folders you will see will not exactly match my images.

Following are the steps taken for recovery:

1.  Do a Finder search for iPhoto Library and select it when it shows.  (Do NOT choose Library.iPhoto).

2. Highlight the file when you find it with your mouse or track pad. press Control key to reveal hidden files and folders.

3.  Press  your Control key while iPhoto Library is selected and “Show Package Contents” will appear within a large menu.  Highlight “Show Package Contents” so we can see what is inside that folder.

4. Mouse click “Show Package Contents” and it should open to show a whole long list of more files and folders as seen below.  Select “Masters” folder and open it.

5.  Make sure you open “Masters” and once you do, it should show another long list of sub folders with year dates.

6.   Inside each year folder will be month and day sub folders and then your .jpg images.

I hope this works for you.

Aside comment:  I keep running into people who have important photo images on their cell phones and computers with no backups.   You might think we have vastly improved our technology with digital cameras but film cameras archive way better than digital.  Think of hard drives as light bulbs; they burn out.  Think of solid state hard drives as longer life light bulbs.  DVD disks are a long term possibility but not as good as film.  Right now, I have no idea of how to solve this archive issue other than shoot film.  When storing DVD disks and film, make sure you treat these media properly so you can retrieve the data way into the future.