Ok first open the webpage where the blob image is and Click inspect, then go to Network
after that refresh the page while Inspect > Network is open
Then locate the blob image in Network and click the Preview tab to see if you got the right blob
Then Rightclick on the Preview image and download the blob image
Then Locate the downloaded blob file
Now rename it with the proper Extension for the image (.png, .jpg, etc...)
Now rename it and click on yes if it asks you for confirmation
And that's it you have successfully downloaded the blob image