<p>Ha, it turns out I had more than one image titled 'Mystery paddle steamer' and the one I just uploaded a more detailed view of wasn't the one I was being asked about! So here is the correct one, again cropped and uploaded at higher resolution, but still from the original scan I made many years ago. I've tweaked a few settings to make the image somewhat clearer, if a little untrue to the original which can be seen below.
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This is a 3.25" square lantern slide, the original image probably being late 1800s or early 1900s.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/24469639@N00">whatsthatpicture</a> from Hanwell, London, UK
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/whatsthatpicture/7949202054/">Mystery paddle steamer, possibly  "Royal Sovereign" or the "Koh-I-Nor".</a>