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Sure you can use image on website but don't forget to insert alt tag on it. You can even implement some tricks there like adding keyword on alt tags but becareful for keyword stuffing.

Yes, you can point link to authority site like wiki and any other. It should be relevant to your niche.

I don't think this is better idea. Instead of that find competitors backlinks and try to get links from that site.

I think profile link building is dead now. After google's latest update they are not giving much value to such type of links.

It might be a problem if you ping too much forum post at once.