eLearning Alt Text Help

Hi! Can you help me with something? I've sent a similar message to a few of my instructional designer friends, but thought I'd post it here as well.

I have a question regarding adding alt text to images in eLearnings and other mediums. I cannot seem to find a consistent answer. So, I’m hoping you can help me.

I typically use Articulate Rise for our eLearnings and sometimes Articulate Storyline. I have added alt text to all of our eLearnings/trainings. But I have found a few resources that say how I've have my alt text is incorrect. I cannot seem to find a consistent answer and would prefer not to go back through all of our eLearn ings and update them to find out later the alt text is still incorrect. Here's what I've found:

- Alt text for logos should read: alt="_____ Logo" where others say to just have it read: "_____ Logo", and others say it should read: _____ Logo without quotations. If the logo is added for decorative purposes only then you should leave the alt text blank.

I've watched the alt text webinar available on E-Learning Heroes and it say:
- For decorative images, alt text should be nulled out (e.g., alt="" or ""). The alt text should not be left blank.

Which is the correct way to post alt text for logos?

Also, should alt text read: alt="_______" or just "________" (with the description of the image in between the quotes)?

This shouldn't be this confusing, but I cannot find a consistent rule about this. 

Thanks for your help!

Anne