You can easily download threads photos and videos without installing any app using the Threadsvideo-download.com website.
This is a pretty easy trick to download threads images to your phone or pc.

Steps
Click on the share icon on the below of the picture to open options.

From the options tap on copy share URL and the link to that image will be copied to your clipboard.


Next visit https://threadsvideo-download.com and paste the copied url in the text field provided.

Next click on download to save the image.