I’m working on a Twine game in my spare time. I’ve almost got 30,000 words written so far.
I’m at a crossroads where I feel like it’s a lot of text and I could spruce it up with some images, but I’ve always found it tacky the way most HTML games just steal porn gifs and there’s rarely any cohesion between the images you’re seeing.
I’m considering slamming my head against AI image generation to get what I need.
For those who play HTML games, how important are pictures? Will you just read through erotic text, or do you need images?
Well i find it depends on how well you can paint the Picture with Words!
A lot manage to do so, But most don’t! 
I’d say to put pictures in places where you think it Will Aid the Story…
like Say your Main Character Meets Another Character Describe them well Obviously, But I’d say add an image so one can visualize them in the story rather then try to picture them every time the Main Character meets the other!
But other then that I wouldn’t worry too much on adding any other pictures to it Unless Its a Complex Part of the story And is hard to visualize! 
Hello. Images will not be superfluous - on the contrary, they will be able to add a moment of individuality to the game. Of course, if the picture is from the developer, it will only help in the work. Here is an example Corruption of Champions II – FairyHaven. Just pay attention to the game design here. Totally gormanic. (If this is not an advertisement, but just an example)