This task required some crypto and osint skills to solve.
1. Check EXIF of the image, there is a long string in the description field.2. Decode this string with base64, you'll get something like an URL.3. Decode it with as Vigenere cipher, key is `DENIS`.4. Follow the decoded URL. There is Google Doc with table of Portugal kings and something looking like Reddit usernames.5. Open Reddit account of Denis the Poet, check his bio. Learn that he is "dev that loves to share and contribute" (open source, huh?), going by his "first name and dynasty".6. Do a quick Wikipedia search, and learn that Denis the Poet is DenisBurgundy at Github.7. Basen on info from the Reddit bio and posts, open repo called `TheMiracleOfRoses`. From the Reddit bio get info that "The first version is the best" — check older commits.8. There is another base64 string, which gives the flag template: `flag{DaughterName_SonName_BuriedPlace}`9. Use Wikipedia again. Find out that doughter is Constance, son is Afonso and burial place is MonasteryOfSaintDenis. So the flag is `flag{Constance_Afonso_MonasteryOfSaintDenis}`