A B757 WAS SPRAYED FOR ICE REMOVAL AT CVG. LATER ICE WAS DISCOVERED ON BOTH INBOARD WING SURFACES.

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UPON ARR AT THE GATE; WE NOTICED THE ACFT HAD BEEN ON THE GND ALL NIGHT AND WAS COVERED WITH SNOW AND ICE. AFTER PUSHBACK; WE TAXIED TO THE DEICE PAD AND THE ACFT WAS DEICED BY 3 DEICING TRUCKS USING A 100% CONCENTRATION OF TYPE I FLUID. THE DEICE CREW NOTIFIED US THAT THE ACFT WAS 'FREE AND CLR OF ALL ICE AND SNOW.' HOLD OVER TIME WAS NOT AN ISSUE AS THERE WAS NO PRECIPITATION AND WE WERE AIRBORNE WITHIN 20 MINS. AFTER TKOF; WE HAD TO CLB THROUGH A SMALL DECK OF CLOUDS AND WERE ON TOP AT 6000 FT. ENG AND WING ANTI-ICE WAS USED. UPON LEVELOFF AT FL350; A FLT ATTENDANT INFORMED US OF ICE ON THE WINGS. A PAX HAD INFORMED HER. I WENT BACK TO INSPECT AND FOUND A SIGNIFICANT AMOUNT OF CLR ICE ON BOTH WINGS FROM THE WINGROOT OUT TO 7-8 FT AFT OF MID-CHORD. WE EXPERIENCED NO ABNORMAL FLT CHARACTERISTICS AND THE ICE WAS GONE UPON ARR TO LAS. I BELIEVE THE DEICERS THOUGHT THEY HAD REMOVED ALL THE ICE; BUT I DON'T THINK THEY CHKED CLOSELY ENOUGH. THERE WAS A TRUCK ON EACH WING AND BOTH GUYS MISSED THE ICE. GRANTED; IT WAS CLR ICE AND IT WOULD BE DIFFICULT TO SEE WITH DEICING FLUID DRAINING OVER IT. HOWEVER; AS PLTS; WE FOLLOWED ALL PUBLISHED DEICE PROCS AND WERE NOT REQUIRED TO VISUALLY CHK THE WINGS. THE CAPT IS RESPONSIBLE FOR NOT TAKING OFF WITH ANY SNOW OR ICE ON THE ACFT; YET HE'S DEPENDENT UPON THE JUDGEMENT OF THE DEICING CREW. EITHER A VISUAL CHK BY PLTS NEEDS TO BE DONE AFTER DEICING; OR ICE PROBES SHOULD BE USED BY DEICERS TO ENSURE COMPLETE REMOVAL.