Photo thumbnails revert back to originals

[YapperMac]

I have photos extracted from old libraries that appear to be thumbnails rather than jpegs.
Is there a way to revert or convert back to original format??
Please help

 

[Slartibart]

„old libraries” refers to old iPhoto libraries? If yes, sorry to report you copied probably the previews and not the original data. As a quick check to make sure: what is the file size in Finder and dimensions of your “extracted” photos?

 

[YapperMac]

Yep, from iPhotos (rather than Photos)
Unlike JPG which are MB in size; most thumbnails are KB in size

 

[Slartibart]

Yep, from iPhotos (rather than Photos)
Unlike JPG which are MB in size; most thumbnails are KB in size

You copied the wrong files. There is nothing to do besides - if possible - to go back and copy the originals.

 

[chabig]

I have photos extracted from old libraries

You would likely have to go back to the old libraries to find the originals.

 

[RhetTbull]

Yep, from iPhotos (rather than Photos)
Unlike JPG which are MB in size; most thumbnails are KB in size

Do you still have the original iPhoto libraries? If so, you can right click on the library, select "Show Package Contents", navigate to Masters and copy the photos from there. Alternatively, there are 3rd party tools that can export the photos such as PowerPhotos and my own free open source tool OSXPhotos.