"I like taking funny pictures."
Putting の after a verb nominalises it. In other words, makes it act as a noun. So while とる means "to take (a photo)", adding の makes it "taking (photos)". Then it can be treated just like any noun in the pattern "[noun]が好きです". In this case the noun is "taking funny pictures".
So, can は and が be used interchangeably with this type of structure?
Using は and が is not easy for learners. I'm also still learning the differences. :/
"The 「が」 particle identifies a specific property of something while the 「は」 particle is used only to bring up a new topic of conversation." This is how Tae Kim explained it here: http://www.guidetojapanese.org/learn/grammar/particlesintro
I know it's not that simple but this is how it works for me. Wa emphasizes what comes after it. Ga emphasizes what comes before it.
Besides their numerous uses, the easiest ones to help you understand the functions of は and が can be explained simply as は, the topic marker, identifies something that is already understood between both speaker and listener, like a general topic or something already mentioned earlier. が presents new information about what it marks.
I thought 'okashii' was 'funny' and that 'omoshiroi' was 'interesting' or 'fun' (fun and funny are not synonyms.)
Omoshiroi is interesting and funny. A few lessons ago, Duo messed up and put fun for their lessons. On TV and in person, I hear it used for funny mostly. When I use it to describe something interesting, people sometimes mistranslate what I mean. Like saying Japanese traditions are omoshiroi isn't the best thing to say lol...
One meaning of 面白い is "funny." My understanding of おかしい is that its meaning of "funny" stems more from おかしい's parallel meaning of "weird" - so it means "funny" more like "bizarre," while 面白い means "funny" more like "amusing." I could be wrong on this distinction though - both words might just mean "funny" in the same sense!
のが is an alternative form of nominalisation, similar to ことが. There are some scenarios where only のが can be used; some where only ことが can be used. It's all a bit painful and complicated, I'm afraid. This link might be helpful: https://japanese.stackexchange.com/questions/1395/what-is-the-difference-between-the-nominalizers-%E3%81%93%E3%81%A8-and-%E3%81%AE
Because おもしろい is an い-adjective. You can put those right in front of nouns without additional particles. の is reserved for chaining nouns together.