http://imgur.com is a great place to host images. They offer many different types of links, including "direct link," which is what you want. You can sign in with your Google account, so it's super easy to get started.
Instead of adding your icons one at a time, you can create a set and upload the entire thing at once.
Example:
If you have four images on
imgur.com, at the following links:
You can create a single line of code (called "JSON," which stands for JavaScript Object Notation) like this:
I recommend you use
http://jsonlint.com to validate the string. It can be tricky to get all the wobbly bits in the right places. (Paste in your string and click the "Validate JSON" button. If it says "Valid JSON," you're good to go. If it turns red, your brackets don't match or are missing or something.)
On your Google calendar, click the green down-arrow in the event flairs widget. (See below.) It'll prompt you for a "flair set description." Paste in that single line of JSON code you created. Click OK. Ta da! If your icons aren't right, you can click the trashcan icon to delete all the icons and try again. When it's all the way you want it, save that line of code in a text file somewhere in case you need it again. You might want to add an icon or they might get wiped out again.

I hope this helps. Let me know if you have questions, and I'll try to help.
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