Is my damaged passport still valid?

Here is my personal experience. My passport has been damaged in a similar way by a US immigration officer four years ago, although it's slightly smaller :

It has not been a problem for getting a US visa, a Russian visa, and for travelling to Europe, the US, Canada and Brazil. The only time someone noticed it is when flying Emirates Airlines to Japan : during check-in they made me sign a waiver saying that it's not Emirates' fault that my passport is damaged, in case I'm refused entry because of it. But it wasn't a problem at all when entering Japan.

From what you've described and the shown in the images, your passport has not been invalidated. Damage sustained while travelling is of concern but, fortunately, it is a corner torn from an unmarked page.

Generally, passports are automatically invalidated when they are significantly damaged, particularly when the data and chip portions are no longer clear and readable.

If you're still on your travels, it shouldn't be necessary to replace your passport although, if you're still concerned, you can always stop in at your country's nearest embassy or consulate for verification. Otherwise, wait until you return home to ask whether a torn page merits the expense of replacement.