Dumb question: how to get custom icon/avatar on Apple ID?

You have to be a Level 3 then you can upload one from your Mac.

Here's what Apple says:

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Custom User Icons

If you want to be a true original, you can—at least as far as your user icon (aka avatar) goes. Once you reach Level 3 status, you can specify a custom user icon that will override any other previously selected icon.

Before we show you how to do this, please note the following restrictions:

An icon cannot exceed 36 pixels wide by 36 pixels high in dimension.
The maximum icon file size is 10KB.
An icon can be either JPEG or GIF format only.
Offensive or abusive icons will be removed and your Discussions privileges may be revoked.
Do not use any Apple image that may cause other users to confuse you with an Apple Employee.
Do not use any copyrighted material for which you do not have expressed written permission to use.
To upload a new icon or replace your current one, do this:

Click Preferences in the sidebar to go to your preferences page.
Click the Icons button to view your icon selections.
In the "Your User Icon" section, you should see an area for custom icons. If you have already uploaded an icon, you will see it here.
Under either "Replace custom icon" or "Load custom icon," click the Browse button and navigate to your icon.
Click any other preference button to set your custom icon.
To remove your custom icon:

Select the button labeled "Remove this icon." Click any other preference button to complete the removal process.

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Can I convert my photo to icon? For Discussions?
Thank you

Is this a "level 3" question, Pancho?

Sure you can, just use Graphic Converter or a similar program. Make sure you make it within the size limitations specified.

Rj Thank you!
Rollin, I never pretended or wanted to be "level 3", I want only to learn and try to help someone at discussions, I know in some areas my knowledge is very limited, I am musician and my English is not good. Thank you