In MRL-0004, it's said:
Bob wishes to send 0.75 XMR to Alice, and will pay 0.01 XMR in fees. The Monero that Alice receives, 0.75 XMR, will be delivered as two new unspent transaction outputs with amounts 0.7 XMR and 0.05 XMR. Further, an output of 0.01 XMR must be delivered as a fee. This leaves 0.24 XMR as change, which will be delivered to Bob in two unspent transaction outputs of amount 0.2 and 0.04 XMR each. At some point in time later, Alice realizes she has 0.75 XMR and decides to go spend it some place. When she does so, both of her outputs, 0.7 XMR and 0.05 XMR, are included in her ring signature. An observer could then look at her ring signature and draw a conclusion that whoever signed that ring signature probably is the owner of both the 0.7 XMR and the 0.05 XMR.
Is it possible to trace an output among many transactions like this? Because when I spend an output and then inspect the transaction (like in here), I find the "key image" field of each output completely different from the transaction that created those outputs in the past. Is there some other field that's not shown here that uniquely identifies an output?
And if the outputs can be traced, then the mentioned attack seems almost trivial to carry out. Am I missing something here?