You should update your seo knowledge , as google checks for couple attributes where alt text, although is recommended, isn't the only one important parameter. Filename plays a more important role, along with floating text around it.
alt text is important for screen readers as well (WAI-ARIA, accessibility and that kind of stuff). in terms of seo alt text plays its role, if you use schema.org itemscope you can tell google what the image is and alt text helps to index it correctly. Important if you are keen on being first everywhere
It's always accessibility+web standards VS SEO
All factors matters in some way. But who's testing novadays his website with disabled images, JS, css and so on ? This takes time.
To be honest I loose interest in writing anything right after I think about all this dang seoshhhht I'd need to fulfill.
It takes a lot of time.
The more, I've got some paid stock photosalong with those I've created by myself I'm going to use. And I wouldn't want them to be found in g.images, grabbed for free and reused - which is a daily practice in inetwebz. Enough that the content I create meets the web standards.
But all depends on goals somebody wants to achieve.
I wanted to have at last a personal blog