From Intense Ragnarok Online Wiki
This happens when running RO using a non-standard aspect ratio. RO is an old game, and it pre-dates the whole widescreen scam*. On some systems, this results in screenshots not being taken correctly when using aspect ratios (the ratio of horizontal:vertical window size) other than 4:3.
1) Open setup.exe / iROSetup.exe in the ragnarok folder. From the second menu, select a resolution with a 4:3 aspect ratio. Typical choices are 800x600 (for small screens), 1024x768, etc. 1200x1024 also probably works, as despite having a 5:4 aspect ratio, this resolution was widely used while RO was in development. Check the box for windowed mode (because on any LCD widescreen monitor, running with a 4:3 aspect ratio will result in the game being stretched unacceptably.
2) Click OK and restart RO. --Credits to iRO
Solution 1: Change your resolution
Change the resolution of your RO to one that isn't widescreen. (640x480, 1024x768, 1280x1024)
Solution 2: Run in Full Screen
Try running your game in full screen mode. If you're currently running on full screen mode, switch to windowed mode.