I agree with the fellow who says it doesn´t make sense to highlight a single word, considering it´s a part of composed verb. Besides, the reasonable explanation I found out was the following : Erkennen = Recognize smth/sby (which you don´t know yet). Wiedererkennen = Recognize smth/sby you already had a previous knowledge, even though it´s not translated literally in English.
Ich hatte mit Angelina Jolie zwanzig Minuten lang gesprochen aber ich hatte sie gar nicht erkannt. Wie peinlich!
Ich habe Angst, dass ich meinen Neffe am Bahnhoff nicht wiedererkennen werde. Ich habe ihn nicht seit zehn Jahren getroffen.
In the second sentence we realise the speaker could at some point in the past recognise his nephew. The person who met Angelina Jolie would not have recognised herhad this happened at any time. Anyway the default is to use erkennen, just add a wieder- when there is an "any more" concept
I believe the opposite of what you are thinking is what really happens in German. (It seems that only the verb "sein", "to be", follows the logic by which the negation particle is attached to the verb.)
If you say "Ich mag nicht dieses Hemd" you are emphasizing the last part of the sentence ("I don't like THIS shirt, can't you see which one? Are you blind?")
However, I am not a native German speaker. That's only what I think at the moment. :-D
From the comments, I understand that wieder is part of erkenne. However, usually when DL introduces split verbs they mention it in the drop-down translation of the word (as erkenne...wieder). It didn't do so this time and I think that's where everyone's confusion stems from. Is it similar to "could have recognized" or am I way off?