The photo may be grainy on the page you are looking at because the photo is in multiple Categories.
The size of the photo is determined by the Primary Category the item is listed as. For example if you nave a News Item in the School News and the Homepage News and the Primary Category is School News but the Website has Homepage News on it then depending on the photo size of the School News is how it will be displayed on the Homepage News. So if School News is 320x320 and Homepage News is 980x980 it will appear grainy because it is actually pulling a 320x320 sized image and stretching it out making it grainy, because the Primary category its pulling form School News has a smaller image setting. To fix this you will need to make the Primary category the one you want to display the larger less grainy image.
You can make the same story in both categories but this will not update from one another if a change is made.
To find the Primary Category pull up the Item by navigating to onMessage Content Content Type (News etc) Click into the Category the Item is in Click the Editing Pencil on the Item You will see the Primary Category Listed as shown here: