Hints for solutions:

Solution 1: Hint 5, Hint 2
Solution 2: Hint 2, Hint 1, Hint 3, Hint 4

Solution 1, steps:

1) find the 2nd puzzle image (header2.jpg)
2) find pR9Et giveaway code in the 2nd puzzle image meta data (exif)

Solution 2, steps:

1) find _R_Et giveaway code in the puzzle image meta data (exif)
2) use a non Microsoft web browser (so not IE, Edge), check the page source of the main website (pesc0tro . netne . net) and find out there is a hidden html added:

<div id="pesc0tro_secret" style="display: none;"><p>hm</p></div>

after each refresh of the page the number of 'm' characters in the 'hm' is increased by 1 up to the 9 where the 'interesting...' is added too:

<div id="pesc0tro_secret" style="display: none;"><p>hmmmmmmmmm interesting...</p></div>

after next refresh the cycle repeats so this should tell you that one out of the two missing characters is '9'
3) use a Microsoft web browser (IE or Edge), check the page source of the main website and find out the hidden html is not added there but when you refresh a page each 9 times, the following hidden html is added:

<div id="pesc0tro_secret" style="display: none;"><p>p</p></div>

this way you should know the last missing character is 'p'

Regarding Solutions 2, all people found out the correct answer just with the 2 steps as they used the letter 'p' because of the html tag <p> there. It was a coincidence, I should've selected different letter for this solution, my bad :)

During the giveaway it appeared my website had been locked. I tried to wait to get it unlocked but it seems this is not going to happen, this was a free hosting so I just created a new domain where you can test the above: http:// pesc0trohmmpuzzle . comli . com (remove spaces)

What you could learn from this puzzle, and potentially use to solve other puzzles, not only by me:

1) It's possible to add/hide some data within image files.
If you download the main puzzle image (header1.jpg) you should be able, without any tools, to see the meta data tag I added, just by checking properties of the file, however, Windows and other OS most probably won't show there all meta data possible. This is exactly the case for the second image file I prepared (header2.jpg). To view meta data of image files you don't even have to use any software as there are many online services where you just paste url of the image and you'll see all meta data, however, I tried some tools and not all of them show the giveaway code for the header2.jpg image. The tool I can recommend is Jeffrey's Image Metadata Viewer
2) It's possible to create a website to look differently, have different features available to some browsers only
Even though the puzzle I created required (in fact it didn't but never mind) to use a web browser by Microsoft, I strongly suggest not to use their browsers. This is mostly valid for older versions of Internet Explorer, not sure about the recent ones, but it was always a nightmare for web developers to integrate modern designs to work under IE so be aware that if you use IE browser, the websites you visit may not only look worse comparing to what they look like on other browsers but also you may not have access to all website features.

View attached image.