Does this occur if you start Thunderbird in Safe Mode: https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

I 've just tried. Same problem :(. I started TB in safe mode using "shift"

Does anybody have further recommendations? Thank you!

As a test. Could you resave/rename the image, so it is a.jpg image and not a .png image.

then do the same tests. Report back on results.

Seems like it does not matter what extension the file has. But I made another test. I 've chosen a mail for testing with a picture in it's body. I clicked reply: so I have checked that the problem occurred (I see only frames). It is important to mention that ThunderBird did not warn me about anything. BUT, if I take the same mail and save it into the file, then open it and click reply, ThunderBird warns me that it has blocked the uploading of a few files into this message (see, the attachment, the language is Russian, but I am sure you will understand what this warning means). So, if I click "unblock" the image appears. I guess the same thing (blocking) happens when I just click reply on any mail with attachment. Do you know how to switch off this block? Thank you.

Thunderbird by default will block any image which contains remote content. This is done for reasons of Privacy. Info on 'Remote Content': https://support.mozilla.org/en-US/kb/remote-content-in-messages

I know about the remote content. This warning usually appears when you receive a subscription or SPAM email with a web-page-like body: in that case, ThunderBird blocks remote content. BUT I am speaking about normal emails from real people. They put their screenshots like ctrl+C ctrl+V or drug-n-drop. These pictures appear in the original mail but do NOT appear when I do reply. Please, see my the very first post. This problem began to occur, I guess, when I have updated my TB from the version 38 to the version 52.

Seems like it is a bug of version 52. Does anybody have ideas? If not, I will submit a bug report...

Try:

• 'Menu icon' > 'Options' > 'Options' > 'Composition > 'General' tab
• click on 'Send Options' button.

• Do not select - uncheck if selected: "send message as plain text if possible".
• click on 'OK'

• Select the 'Display' > 'Formating' tab
• click on 'Advanced' button

• Is this option selected?
• 'When possible, use the default text encoding in replies'
• If this is selected, uncheck that checkbox
• click on 'OK
• click on 'OK'

Restart Thunderbird.

Create a new email and send to yourself and any other email address you own. then test replies on the received email.

Hello! Thank you for your response. 1. I have unselected this "send message as plain text if possible". 2. "When possible, use the default text encoding in replies" had been unselected already.

But it did not help. The problem is the same. Please, note, that if I send email to myself (from my ThunderBird), the problem does not occur.

The problem occurs if I reply to someone's email (I do not know that email client they use (I tried to save this email to the *.eml file but I did not find any text like "User-Agent" inside this file).

If you need more information, please tell me. If you need, I may send some useful information from the *.eml file

Are there any other ideas? Thank you.