Some examples to see the difference (not much, it;s mainly how you want to store thepictures).

This page on the web site has the pictures shown from Flickr, since the pictures belong to other people who have allowed us to show these pictures.

This page on the web site has the picture stored on the web site, since it was taken by the author of the page.

The examples below use the same picture, stored in different places:

The picture on the right is on Flickr, clicking on it will take you to its page on Flickr.  Dronie
11 years ago ago at , Framingham, Massachusetts, United States by Tim Booth.

The picture below is stored on this server, using the large thumbnail - clicking on it will take you to the larger version of the picture,  also stored here.

And the picture below is the same picture stored on an external web site, linked via its thumbnail, also stored on that site.

(This picture isn't anything to do with orienteering, it's a dronie, note that the Flickr example displays the title held on Flickr (also "Dronie") if you hover over it.