[Gimp-user] how to mingle the edges of picture clips?

[Don]

I am very very new to Gimp and graphic design.  I think this is very basic,
but don't know the professional terminology.

Please take a look at the following picture,

http://www.peteconstant.com/assets/images/Web-Banner-Raw3-Dan1.jpg

You can see that different pictures are mixed into this web banner, and they
don't have a clear edge between them, in other words, where they get joined,
the color gets blurred.  I am sure this is easy and very very basic, but
don't know how to google out since I don't know what this technique is
called (I think this is an area which google needs to work on, i.e., how do
I google if I don't know what a concept/entity is called).

Please kindly advise.  Thanks a lot.

Disclaimer: I have nothing to do with peteconstant.com, the banner is simply
a google search result and an arbitrary pick from a bunch.
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