As you already know, you can fashionably display the categories by using the Pixelgrade: Categories Images widget from Appearance → Widgets. The image of the category will be represented by the first post’s image.
However, you can have a dedicated image for a certain category by following these simple steps:
- From your WordPress Dashboard, go to Plugins → Add new plugin.
- Search for the Category Icon plugin, install and activate it.
- Next, go to Posts → Categories and hit the Edit button on the category you’re after.
- Select the Image field and assign the desired image and you are ready to go.