How to use chrome.storage in a chrome extension using a variable's value as the key name?

Use a named object, not an anonymous object, and set a member variable using square brackets:

var dataObj = {};
dataObj[imageName] = myDescription;
chrome.storage.local.set(dataObj, function() { /*...*/ });

It's not the most elegant looking code, but it's the only way to do it.

In ES6, a slightly shorter approach is to use an object literal with a dynamic property name:

chrome.storage.local.set({
    [imageName]: myDescription
}, function() { /*...*/ });

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