Translation:This blogger uploads photos of his dishes.
You pretty much said the same thing I did, and I said nothing about "posts" being acceptable. I said nothing about "uploads" being acceptable for that matter, since neither is correct.
I can start a web server on my computer and put photos online that are on my computer, and not have to upload anything. I can even open a port to allow access through my firewall so they are also available over the Internet.
Putting things on line is not the same as uploading. Neither of them is the same as putting something on the Internet, except that something that's "on the Internet" is online. Putting something on the Internet does not necessarily mean putting it on the Web.
Duolingo constantly uses terms that are not interchangeable as if they were. I understand that a lot of people don't know the difference but that's no reason to teach things incorrectly.
It should help your French to know that Internet, Web, post, and online all have distinct meanings and all have specific translations in French. You should not use them interchangeably in English or French as Duolingo does.
I think it's also fair to say that many people who learn foreign languages are interested in languages in general, and one thing that learning a foreign language can do is help people with their native language by covering certain concepts.
In this case, "posts" is a better term, because I can put something online simply by giving a specific permission on a server. I could email you a link to a document that's available online. If I post it, the implication is that it's available on a web page or app and is now visible to people who use whatever means is typically used to see content of that nature.
However, the French statement merely said that something was put online, so the most accurate translation would reflect that, even though it's likely that the person actually posted it. Technically that means it was put online, but that was only part of what was done.