Alt Image Text

Does anyone understand this well enough to ELI5? I'm a photographer. The self-build website instructions (Pixieset and Yoast/WP) say "if the image is purely decorative, leave it blank. They also discourage "keyword stuffing". Okay... as a photographer, most of my images are purely decorative. They are art. The art is decorating the page. The blog post showing off the art is a page full of decorative images with some basic storytelling paragraphs. AND - all the images are from the same wedding event, so describing again and again "table decor at \_\_\_\_\_ wedding venue" is going to be perceived as keyword stuffing, right? But as of right now, (according to semrush) I rank nowhere and Pixieset has identified 3566 images without alt text and has put that as the reason I'm in the yellow for SEO. I'll be googling YouTube videos to try to understand this better, but if any of you out there truly get it, I'd love a more nuanced explanation.