You can only experience the HDR effect when running the app, because it is not visible in the screenshots above. The latest images are taken only a few hours ago on planet Mars by NASA Perseverance Rover currently driving in and around Jezero Crater.
This is currently the only app showing real Mars images in high dynamic range (HDR) and color calibrated for human vision to bring the experience, human explorers on Mars would have themselves, to iPhone and iPad. To navigate through the sols (days on Mars since landing) and images of each sol, either tap on the two up/down buttons on the right side or swipe horizontally or vertically or rotate the wheel with the sol numbers. Double tap or pinch with two fingers to zoom in and out.
The images are taken by the 20 Megapixel Nacvam pair inside the rovers "head" 2m above the surface, the two 20MP front and rear Hazcam pairs near the ground, Watson Camera on the robotic arm and Cachecam in the underside sample storage bay.
The HDR effect is visible on iPhone X or newer models or iPad Pro since 2018. On other devices the images are shown in standard dynamic range (SDR).
The raw image data used to produce the color processed images is publicly provided by NASA / JPL-Caltech. The color processed images shown by the App are separate derived data products and created by the App authors system.