Block the communities you know are going to be an issue, there's no automatic backend filtering of pornographic images, there's the blur NSFW option which might be helpful at not displaying stuff while allowing you to see if that's something you want in your lemmy experience.

you could make a separate account for that

If you want to retain the idea of one account just make sure you check “blur nsfw”. This way you can still view the front page but if you see a blurred picture you can either ignore it. Then you have the option to look at the community it’s posted to and know if it’s porn or just bad language etc.