Process of inspecting an image quality of an action camera is quite similar to video quality checkup. Simply, you should find an uncompressed, unedited, original, straight from the camera image sample and preview it on your PC. Images that websites (including ours) place online are compressed in order to load faster on the web. Therefore, it is once again recommended to find an unedited JPEG or RAW image of the camera you are interested in.
Since action cameras have fixed-focus lens, the first thing that you should look at is sharpness. Is the image clear enough even when zoomed in for 2x-4x times? If you’re satisfied with a result, pay attention to colors. Are they natural, vivid or over-saturated? Also make sure to find a sample that shows image quality under a direct sun-light and at night. If you really want to go crazy, check if there are too many dead, white pixels in low-light.