stigcq

A plugin offering a widget showing recent photos in posts. It can be configured 
as for how many photos to show, the title on the widget and max width and height for 
thumbnails.
The thumbnails links to the post where the photo is showing. They show a mouse over 
effect with bigger version of the photo in a tooptip.
It has option to exclude photos from the view.
It has only been tested with WP 4.2, it might work with lower versions.

Recent photos widget

A simple widget which shows thumbnails of latest photos in posts

Konstantin Kovshenin

Use this widget to display your Flickr photos in your sidebar, via a Flickr username or a Flickr RSS feed URL.

Quick Flickr Widget

Display your Flickr photos in your sidebar.

Recent photos widget vs Quick Flickr Widget