IHG already has this sorted.
In the example given, choose "Select pics". Click on "Clear all" - all the ticks disappear. You'll notice that the first pic is highlighted in blue. Using the scroll bar on the right scroll down until you see img.yt. Hold down the shift key and click on the last chronos entry - ALL the chronos are now highlighted in blue. Right click and choose "check". All the chronos will be downloaded.
If you prefer to download from img.yt hit "Clear all", scroll down to the first img.yt, click on it, hold down the Shift key, hit "End" to highlight them all, right click, etc.
In the the "Select pics" dialogue the standard Windows keys - Shift to select a range, Ctrl to select individual items. End, Page Down / Up and Home are available for navigation.