@bocaholly - I have always seen just exactly what Andrew said.

However - ( Windows 7, Chrome browser ) I can right-click and download the "image" by asking to open image in a new tab - and that's the first step - what it actually does is download your image as a .tif file, and saves it .  That download file will then open cleanly in a browser window.

I did mean to bring this to your attention as well, but forgot !

Technically, though, I don't quite understand why it doesn't open directly....  anyway - I mean it is a permitted file type...  but wait - 

No - I don't actually see ".tif" as a recognised file type in the list....   but then, why is WordPress allowing it ????  Mystery to me...   

We can ask Pierre @Fiddlerman to allow .tif files - we got MuseScore .mscz added some time back, so it is configurable....

Perfect @bocaholly - reasonable work-around

I go back to one of the earlier points I made about .tif files not being a permitted file type (within the WordPress/Simple press configuration for the forum - it is a perfectly allowable file type - it just needs to be "permitted"), and to get your image posted, what appeared to be happening is that it was pasted into the post, and not actually uploaded to the server.  

I'm also wondering why some browsers show it, and some don't - well - let's not get overly technical here - but - if you inspect the forum HTLM source for these posts (Holly's and one of mine) you'll see that Holly's post includes a "base64" encoding of the entire image - i.e. pasted, not uploaded, into the particular post.   If you inspect the post where I placed a .jpg, you'll see it appears as an HTML link to an uploaded file.

Now - some browsers will be perfectly happy to "interpret" a stream of embedded data within the HTML and recognize it as a .tif image, and display it on-screen. 

Other browsers will not - and it comes down to various "customisations/enhancements" made by the browser designers, rather than actually doing something that breaks, or doesn't meet, the HTML5 specifications.

Here's what you see when you inspect the HTM source for Holly's post - the actual image data is physically embedded into the HTML stream - and of course I have "cut it" - it goes on for ages - the gobble-de-gook is just the ASCII representation of the base64 encoding of the raw binary data belonging to the image.

If you now inspect the HTML source of a .jpg I uploaded, you do not see the raw image data in the HTML stream - you see a link to an uploaded file.   Haha, I obliterated my forum user name - pointless really since anyone can view the HTML source anyway - 

Now - there is nothing overly "special" about .tif files - it's just another image format, capable of being viewed by ANY browser as a FILE LINK - it's just that some browsers don't have the browser-specific customization to interpret an embedded stream of image data.

The bit that "gives it away" is that in my posted .jpg file you see the HTML - 

<img src="https://fiddlerman.com/wp-content/forum-image-uploads/madbill/2018/12/_thumbs/_extension_err.JPG" class="sfimageleft spUserImage" title="extension_err.JPG" alt="extension_err.JPG" />

which is just a link to the uploaded file, and in Holly's you see

 <img src="data:image/tiff;base64,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....

and on and on...

..which is clearly embedded data, and not a link - and IMO that's what's throwing some browsers.

I go back to my original point - it looks like the image is pasted (i.e. not actually uploaded as a file), and once .tif files are made a "permitted file type" for upload through the WordPress/SimplePress settings for the forum, it should be perfect, and viewable on any browser....    

Sorry - I was just bored and trying to find something interesting to do over my first coffee of the day...