identify a word in an rss feed and replace with an image

I have an rss feed coming into a widget. the feed tells me the current uk threat level – Low, Moderate, Substantial, Severe, Critical.

The threat level appears as part of a sentence, i would like to be able to recognise the threat level and replace it with an image.

So instead of the feed in my widget saying ‘The current Uk threat level is – Severe from blah blah……. I would like to replace the whole sentence with an image.
I have different images for each threat level so I need to be able to find a specific word, in this example Severe, and replace with a specific image…

I have tried using a plugin called Word Replacer which does work to a point. It will recognise a specific word and replace it with another word of my choice. Works fine but I cant figure out how to replace the word with an image URL.

Anyone got any ideas?
my url is https://bit.ly/1MA0V4j