Do you have a Backup for your Lightroom Catalog? Check under Pictures>>Lightroom>>Backups(Default location)
Or if the images are missing refer Adobe Photoshop Lightroom Help | Locate missing photos
You need to locate the Catalog "Catalogname.Lrcat" file to recover your images.
Please search your computer for " *.lrcat "(with Asterisk and without quotes)
Hope this helps
Thank you for your kind information. This is what I want to know!!
I could download "ExtractPreviews.lua", however, I could not find suitable folder
to copy the script.
In case of my PC (windows 7, Lightroom 5.6), it seems that the script should be
copy to "/Users/[user name]/AppData/Roming/Adobe/Script", but it doesn't work
Dear Akash Sharma
Thank you for your information.
Since my HDD has crashed, most of data, including Ircat data, has completely vanished...
By chance, only Previews.Irdata is stored in the SD card.
For this reason, I would like to at least recover thumbnail data from Previews.Irdata.