To upload a good quality image, this must be a maximum of 20% text. Also, stretched/cropped images can flag as low quality, with the dimensions in mind, remember that customers who look at your event may be viewing it on their phone so an image with text on would be difficult to view.
Sometimes, a basic image of the crowd at a venue or a band photo is beneficial as the event information is alongside the image therefore unnecessary to fill the image with details of the event itself.
If you are still struggling to get a good quality image, keep an eye on the ‘7 ticks’ and any red alert messages that may appear on the ‘Manage event’ page under your event details.