My MAC can't find the library


I was simply trying to copy all my pictures from my C: drive to an external hard drive as backup but something went wrong.

I copied first 2 folders full of pictures that were on my desktop to the external  hard drive and I had no problem. then I went in to the picture folder and copied everything over the external hard drive. Now when I try to access the pictures in my local Mac I receive an error saying: Photos cannot find library " Photos Library.photoslibrary" This library was last found on a drive named "My Passport for MAC". Please attacehthat drive and click "Try again" if we attaché the external USB drive and click ok we can access the pictures.

But what went wrong? I didn't cut and paste the pictures to the external USB drive, I only copied them! infact the c: on my mac is still completely full. Why I can't not access to the picture anymore ? and how can I fix this issue ? do I need to copy the library back ? from the USB external hard drive to the Mac ? Can someone help me with this issue please providing step by step, I am not a MAC person.

Thank you
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See this Apple KB about designating the system photo library:
ItaliabellaAuthor Commented:
hello and thank you for your important imput. I read the two article but I am not sure if I can reverse what I did. Basically how can I fic the fact that the laptop open up when I click photo library instead of telling me that it can not find the library and ask me to insert the Eternal USB drive ?

Thank you for your patience...
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Eoin OSullivanConsultantCommented:
Italiabella .. please read this carefully

When you copied the contents of the Pictures folder to the external USB drive you copied a file called "Photos Library.photoslibrary" which is actually a folder which contains the entire Photos album.

The first thing to do is ensure that Photos is NOT running .. and if it is QUIT
Then look in the Pictures folder in the home folder on the hard drive of your Mac (what you call the C drive) - check that there is still a file called "Photos Library.photoslibrary" there also.
If the "Photos Library.photoslibrary" is still in the Pictures folder then you can simply make Photos use that one as default instead of the one you copied to the external USB ...
Just hold down the ALT key on the keyboard and then click the Photos icon to open that application.
A dialog will appear where you can click the Choose Library button and browse to locate the "Photos Library.photoslibrary" file on your HD and it will become the default album you open.

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David AndersTechnician Commented:
A completely full hard drive will generate an error message when the free space falls below 2 or 3 Gb.
Knowing the size of the hard drive and the free space available would help diagnose. Photos indicates you are running Yosemite OSX. iPhotos was the app on previous OSX versions.
Holding OPTION key down when starting Photos will allow you to choose the library to open, if you have deleted or overwritten an existing library, you can create a new one.

Google "photos" to see the articles about Photos on Macworld.

If your photographs are important you show have three copies - HD, external HD and internet is often recommended.  offers a free 1Tb storage space for photos
ItaliabellaAuthor Commented:
Einosullivan: thank you for your baby steps. I feel much more comfortable now in fixing this issue. I will let you know everybody if I am successful or not.
Eoin OSullivanConsultantCommented:
Also note the first point made by davidanders. If your HD is nearly full you might need to free some space and empty the trash.
ItaliabellaAuthor Commented:
everyone, following your precise instructions I was able to solve the problem. Thank you everyone.
excellent Job!
ItaliabellaAuthor Commented:
thank you everyone
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