Facebook says glitches affecting its platforms have now been resolved.
Users across the world had been unable to upload or view photos, videos and other files.
The problems had affected its Facebook, Messenger, Instagram and WhatsApp apps.
"The issue has... been resolved and we should be back at 100% for everyone," it tweeted. It added that an unspecified issue had been accidentally "triggered" during "routine maintenance".
Facebook has more than 2.3 billion monthly active users and Instagram has one billion.
In some cases, users were shown grey boxes annotated with text explaining what the firm's image analysis software had suggested to be the contents of the original photos.
Rival platform Twitter also had issues, with some users not able to send direct messages or receive notifications for a time.
The company apologised for the inconvenience, tweeting at about 23:00 BST: "We're almost at 100% resolved. There may be some residual effects for a small group of people, but overall your DMs should be working properly now. We appreciate your patience!"
The latest problems followed earlier disruption on Tuesday when Cloudflare - a company that provides internet security to website operators - suffered a fault of its own that caused thousands of websites to display "502 errors" when visited. The US firm has since published a blog blaming a flawed software deployment.
"Our testing processes were insufficient in this case and we are reviewing and making changes to our testing and deployment process to avoid incidents like this in the future," it said.