Rotate and save the image in portrait orientation. In Thunderbird's insert image dialog, you should see the dimensions of the image. In portrait, the width is shorter than the height. This is displayed on that dialog before you insert the image and a small preview (thumbnail) will show you how the image is going to appear in the message.

In Windows 10 a downloaded image from my camera is automatically oriented correctly. But even if I deliberately rotate it again it still will not appear in portrait orientation in the Thunderbird preview, even if I change the dimensions manually. This was never an issue in Windows 7. As I said, the photos that I copied from my Windows 7 PC to the new Windows 10 will stay in portrait orientation, just the new ones that I have added will not.

I don't think this is a Tbird problem since other portrait images display just fine in Tbird. It must be something in the image files or the import process used to fetch them from the camera. Which program are you using to import them from the camera?

I am using Windows 10 pictures. I don't know of any other means to import from camera. I guess I have to get help from Microsoft.

There is no Windows 10 app called Pictures. If you mean the Photos app, its import feature does not have an automatic orientation option. However, as per this thread, File Explorer may automatically rotate the images for display only. The files themselves are not rotated, just the view in File Explorer, so that if you open the same image in a third-party app, they appear in the file's original orientation. This is causing confusion among users. You can try a third-party image viewer like Irfanview to open the images and confirm that they truly have been rotated or not. My guess is that they are not.

Thank you Stans. I found that if I don't copy it from camera directly to photos but choose to 'edit' it first in photos and save it from there it works. It is a bit of a roundabout way of doing it but I will have to live with it, I guess. Have a great day, Stans.

You can bring back the Windows Photo Viewer too. I hardly use the Photos app, I detaste it!

Thank you for bearing with me Stans. It looks like I would have to know a lot more about registry functions and how to mess with them. Would I be able to copy the photoviewer.dll from my windows 7 PC and install it on my new one? I did try and got the warning:

You are attempting to open a file of type 'System file' (.dll) These files are used by the operating system and by various programs. Editing or modifying them could damage your system.

So, what should I do? Should I click OK and hope for the best? I am just not savvy enough for this sort of thing. I can't believe that Microsoft is ignoring the hundreds of pleas for getting windows photo viewer back.

No, don't open the Registry Editor and don't copy or open or edit the said dll file. The dll file is already in place in Windows 10. It was never removed from its original location. It's still in the same place that it used to be in previous versions of Windows. Don't click OK. Cancel any such dialogs, instead, go to OPTION TWO of that tutorial using the link https://www.tenforums.com/tutorials/14312-restore-windows-photo-viewer-windows-10-a.html#option2.

Under step 2, click the download button then skip to step 5 and onwards. Those steps are clearly labelled and well put, just follow them exactly as stated. The downloaded file is a .reg file and will take care of making the necessary registry changes, all you have to do is download it, open it to "merge" it with the registry and click Yes or Allow on the prompts that follow.

Stans, thank you for your patience, you are very kind. So I did as you suggested, downloaded the .reg file and followed all the instructions and prompts. I've chosen it as my default app. But I'm not sure how to go on from here to make this my new pictures folder. Please advise me when you have time, I don't want to take up your entire day.

Oh, sorry Stans, I see that it is already functioning. So relieved. I won't trouble you anymore. Thank you and have a lovely day.

No apologies necessary. We're here to help whenever and however we can. Good day to you too and you're most welcome.