Up until a couple decades ago, basically all religious texts were distributed without getting consent, giving credit or forking over royalties to their original authors. Rhymes and songs, even images, were observed and then repeated or noted down and spread.
By todays definition, that's piracy. Piracy is exactly the same thing, just in a digital world.
Therefore, if piracy isn't halal, most religious texts and imagery aren't halal either.
Now, looking at it the other way around, to confirm that:
Theft is illegal. So the question stands: is piracy theft?
That depends on the definition of theft. The old meaning of theft, so the thing, probably ruled over in religious texts, is: The unlawful taking of the property of another.
Now, can you take something from someone else, without them loosing it? I'd argue: No!
So, piracy isn't theft. Piracy is copying or repeating.
Well, they have a small point though:
By allowing to upload to a third party image host and allowing to embed images from other sites directly into Lemmy, the load on servers could be reduced while also allowing for larger/higher quality files.
This would obviously come with a downside to privacy.
The current solution would be: upload a highly compressed file to Lemmy and then link to the external high-quality version in the post.
An alternative solution from Lemmy devs could be, to allow external sources and hide the image until the user confirmed they want to load it from an external source. Or just... Add a toggle to settings to automatically load them.
I mean, with federation and all, everything in Lemmy is an 'external' source anyway unless you trust every single federated instance. So why not allow external image hosting/file hosting sites as trusted sources.