You intend to drive into the right lane of the roadway. Are you obliged to use an indicator?

In the photo, on the right, there is sign F-10 "lane directions" showing that before the junction there will be an additional right lane for turning right. Moving into this lane is changing lanes, and you signal every lane change with your indicator. The answer is: yes.

The Road Traffic Act requires you to signal clearly and in good time with your indicator your intention to change direction or lane, and to stop signalling immediately after the manoeuvre. It does not matter that the new lane appears next to yours - you are leaving your lane, so you let the drivers behind you know. The Regulation on road signs and signals says that F-10 shows the permitted directions of travel from individual lanes.

Legal basis: Art. 22 para. 5 of the Road Traffic Act (Prawo o ruchu drogowym); § 72 para. 1 of the Regulation on road signs and signals