Because there seem to be quite a few at the moment, a topic where posts with missing images are collected might be beneficial:
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Thanks @Moin we are having a look
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Something has gone awry with the secure uploads controller. Hopefully a fix will handle them all. 
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Thanks for collecting these Moin; I’ve manually fixed the ones you referenced, and I will work on a fix in the actual code for this soon.
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Should we still report all the topics with missing images and videos? When I was reading the new TOS, I noticed Flagging a post for moderator attention, but I thought I’d wait for the fix.
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Also two missing images on this guide:
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Some more topics with missing uploads
House Ads in the official Ad Plugin
Discourse AI - Helper
Number on the side of categories showing number of topics made in the past week isn't correct - #2 by HamMan2118
Why there is huge difference in Pageviews tracking number on discourse admin dahboard and on google analytics - #52 by Shaneod
Sending bulk user invites
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And this one Masonry Image Gallery
Isn’t it time for a plugin that detects this kind of issues?
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I fixed the images on the Masonry Image Gallery TC. Thanks for pointing it out!
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How did this happen? Might it happen to my forum?
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I looked at simon’s post and checked the first picture (upload://gzHZGGt5fnTVXIlXDYXwTnrYAtp.png).
It’s upload id 263815, is marked as secure, and the access control post is 1368579.
It’s a PM in which I link to Simon’s post and it gets oneboxed. My inference is that onebox causes the PM to to “take over” the uploads.
I don’t think this will happen unless you have secure uploads turned on, and I suspect the damage is historical (rather than a result of a current bug).
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I still think it is a recent issue.
On March 7th I copied What is a Wiki Post? into a PM. I’m sure the images were all visible at that time. Now all images in the public post are broken. But in my copy only the first two and the last one are broken.
I don’t think that images should disappear from public when I copy them to a message after they were published.
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Beginner's guide to using Discourse Themes
Flagging a post for moderator attention
Whitelisted Discourse app with Push Notifications via OneSignal - #56 by tohaitrieu
Discourse CAN show nested replies?
New or unread topics banners cover text at /new & /unread
Header Theme Toggle
Discourse Community Support Program
The Skill Wheel
Our Community Support Experts (and Experts-in-waiting) - #5 by itsbhanusharma
Post your Discourse T-shirt, socks and other swag pics! - #11 by tobiaseigen
User Card Directory - #4 by davidkingham
Header Theme Toggle
Theme component to use "Category icons" in "Events plugin" calendar
Advanced tutorial in French: poll escaping issue - #2 by Canapin
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Some missing images in How much is Discourse affected by a faster CPU? - #27 by codinghorror
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Probably most of these are not relevant because they are outdated topics:
Advanced Search UI
Contributor Interviews – Felix "fefrei"
Beta testing the Android mobile app - #38 by Falco
Discourse index - #38 by erlend_sh
Discourse index - #8 by erlend_sh
Global Discourse Site Directory - mockups
Theme Switcher Component
How to delete a category? - #4 by Mittineague
Spam bots tricking Discourse filter by editing - #24 by codinghorror
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