Lots of things + 中 (chuu) = "in the middle of", "currently", "during", "while", and a broad array of continuous states of action.>自撮り = selfie (jidori)>研究 = research, study (kenkyuu)
You can slap 中 on pretty much anything.>研究中 = (in the middle of) research(ing)
Therefore, 自撮り研究中 is "In the middle of selfie research/study"
You could even place it after 自撮り中 to be "(in the midst of) taking a selfie"
You'll see this a lot in things like>準備中 = in the middle of preparations (becoming prepared, getting ready)>修理中 = in the middle of repairs (being repaired, under maintenance)>離席中 = Away from Seat (a continuous state, so 中 works well here)
Its exact English translation will vary according to context. It's one of those things that despite being simple, does not translate well into English.
You could very well have a sentence like>自撮り研究中、ワイセツな写真を間違えて送ってしまった!>While doing selfie research, (I) sent a lewd pic by mistake!