Helping people with computers... one answer at a time.
Computers are great at making copies of data, and that's very true when you send a message. Two, three or even more copies, some temporary, may result.
When I insert pictures into an email from my hard drive and then send that email, are those pictures saved to my hard drive again? And when I receive a reply with the same pictures inserted, are the pictures now on my hard drive three times?
Quite possibly. Plus one, even.
It's going to depend on your email program, and what options you may have selected, and how the picture was inserted into the email.
Let's run down the variations.
First, there are three ways to include a photo in an email:
As an attachment. This makes a copy of the image and encodes it for transmission in email, and makes it part of the message.
As an in-line image in rich text or HTML format. This also makes a copy of the image and encodes it for transmission in email, and makes it part of the message.
As an in-line reference to an image, typically in HTML format. Instead of including the image in the message itself, the image is referenced by a URL (beginning with http://) to some location out on the internet. The image itself is not part of the email.
In the first two cases, the image is indeed duplicated; in the third, it's not.
If you have a "save sent items" option selected in your email program, then that email - including the duplicated image is saved in your Sent Mail folder. There's your first duplicate copy.
However, if you are using web based email, that folder is kept on your mailing service's server, not your machine. If you're using a desktop email program like Outlook, Windows Mail or Thunderbird, then yes - that folder, and the first copy of your image is on your machine.
When someone replies to your mail, and continues to include the images in either of the two forms above that actually place the image in the email, your email program has no way to know that they are the same image. As far as it's concerned that's a new email with new content. In other words, there's the second duplicate copy of the image.
And again, if you're using webmail, the email is stored on the mailing service's server, not your hard drive. But if you're using a desktop email program then absolutely, that email with its images is stored on your hard disk.
There's one more copy that many forget about.
If you're viewing your email in a browser, then the images are also being downloaded and placed in your browser's temporary internet cache. They stay there "for a while", until the space is needed for other things you browse and view later.
If you're viewing your email in a desktop email program, then recall that I mentioned those images are "encoded" for transmission in email. In order to be viewed they have to be decoded back into their original form. That means that they are placed either into the browser cache I just mentioned, or into the your temporary folder. Depending on how you view the message, close the email program. Depending on how the email program works, those images may or may not be removed after you've viewed them.
And this is all just on your end, when you send. There's no way to know how many copies of a message are made at the recipient's end. (Or, for that matter, on the servers that transport your email, but the sheer volume of email dictates that those be very temporary - there's just not enough disk space to keep it all.)