Autocorrelation and Graphs

[archived_user]

If we are asked to identify by looking at a graph if a time series model has the problem of autocorrelation, how do we identify that?
By definition autocorrelation means that todays value depends on yesterdays value. So lets say that the trend is persistently going up or down, does it mean we have the issue of autocorrelation?
And how a graph without autocorrelation supposed to look like?

 

[archived_user]

Positive autocorrelation looks like this: ________/¯¯¯¯¯¯¯¯¯¯¯¯\_____________/¯¯¯¯¯¯¯¯¯¯\_____________
Negative autocorrelation looks like this: /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
Zero autocorrelation looks like a combination of those.
If the series has a trend, then superimpose those patterns on the trend line.