In FTK, there may be a situation where a carved image displays what appears to be a blank or empty thumbnail, like below:

https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/69009876272/original/blank_grid.jpeg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAS6FNSMY2XLZULJPI%2F20210926%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20210926T165300Z&X-Amz-Expires=300&X-Amz-SignedHeaders=host&X-Amz-Signature=8b398d17f9e06c10e196d521d87f8746e32e6a17e7c9dacf973365845d6b3543

 

However, when selected, you can see the image, as shown below:

https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/69009876273/original/actual_thumbnail.jpeg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAS6FNSMY2XLZULJPI%2F20210926%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20210926T165300Z&X-Amz-Expires=300&X-Amz-SignedHeaders=host&X-Amz-Signature=ef99f7263d5b24ab4f131432a88b24cb2997ac8fa268315db48c00d58bbffa5b


In the above example, the image is carved, and the resolution of the image is 18977 x 23 dpi.
(Based on the image 353 x 371 pixels when converted to dpi, the result is an image that would be about .02 inches wide and 16.1 inches tall.  When converted to a thumbnail, there is nothing to see.)

To see the actual image that the thumbnail was derived from:

1. Select the file in the graphics tab, 
2. Right click on the image in the viewer
3. Click: Size > Use Image Size.