A blank of foldable sheet material for forming a picture frame with picture, the blank comprising: (a) a blank body having a front surface and a rear surface; (b) a central rectangular picture portion provided at a central portion of the blank body and adapted to form thereon on the front surface thereof a picture; (c) two opposite first wing portions (30, 30) extending from two opposite first margins (32, 32) of the central rectangular picture portion respectively; and (d) two opposite second wing portions (30', 30') extending from two opposite second margins (32', 32') of the central rectangular picture portion respectively; (e) wherein each of the first and second wing portions (30, 30') comprises four parallel fold lines (34, 34') parallel with respect to the margin from which the wing portion extends, and defines an elongate frame-simulation panel (40, 40'), a first elongate lock panel (42, 42'), a second elongate lock panel (44, 44') and an elongate end panel (46, 46') in an order from the margin (32, 32'); each elongate frame-simulation panel (40, 40') being printed thereon with a frame-simulating printing simulating a frame surface of a conventional photo frame; (f) wherein the four wing portions (30, 30') are foldable rearwards about the fold lines (34, 34') to a folded position where the four end panels (46, 46') rest on the four margins (32, 32') of the central rectangular picture portion at the rear surface thereof respectively, thereby forming four rectangular tubular frame sections (50, 50') extending along the four margins (32, 32') of the central rectangular picture portion at the rear surface thereof; characterized in that the blank further comprises (g) an elongate panel extension extending from each opposite end of each second elongate lock panels of the two opposite first wing portions (30, 30), and flippable about a transverse fold line formed between the elongate panel extension and the opposite end of the second elongate lock panel of the two opposite first wing portions (30, 30); (h) a slit formed along each transverse fold line at a middle portion thereof; and (i) a tab formed at each opposite end of each second elongate lock panel of the two opposite second wing portions (30', 30'); (j) wherein after the two opposite first wing portions (30, 30) are folded into the folded position, the four elongate panel extensions are flippable 90 degrees about the transverse fold lines towards the two opposite second margins (32', 32') such that the elongate panel extensions are held within the two tubular frame sections (50', 50') formed after the two opposite second wing portions (30', 30') are folded into the folded position, and wherein the four tabs are inserted into and engaged with the four slits respectively at four corners of the picture frame, thereby locking the four tubular frame sections (50, 50') in the folded position. (a) a blank body having a front surface and a rear surface; (b) a central rectangular picture portion provided at a central portion of the blank body and adapted to form thereon on the front surface thereof a picture; (c) two opposite first wing portions (30, 30) extending from two opposite first margins (32, 32) of the central rectangular picture portion respectively; and (d) two opposite second wing portions (30', 30') extending from two opposite second margins (32', 32') of the central rectangular picture portion respectively; (e) wherein each of the first and second wing portions (30, 30') comprises four parallel fold lines (34, 34') parallel with respect to the margin from which the wing portion extends, and defines an elongate frame-simulation panel (40, 40'), a first elongate lock panel (42, 42'), a second elongate lock panel (44, 44') and an elongate end panel (46, 46') in an order from the margin (32, 32'); each elongate frame-simulation panel (40, 40') being printed thereon with a frame-simulating printing simulating a frame surface of a conventional photo frame; (f) wherein the four wing portions (30, 30') are foldable rearwards about the fold lines (34, 34') to a folded position where the four end panels (46, 46') rest on the four margins (32, 32') of the central rectangular picture portion at the rear surface thereof respectively, thereby forming four rectangular tubular frame sections (50, 50') extending along the four margins (32, 32') of the central rectangular picture portion at the rear surface thereof; (g) an elongate panel extension extending from each opposite end of each second elongate lock panels of the two opposite first wing portions (30, 30), and flippable about a transverse fold line formed between the elongate panel extension and the opposite end of the second elongate lock panel of the two opposite first wing portions (30, 30); (h) a slit formed along each transverse fold line at a middle portion thereof; and (i) a tab formed at each opposite end of each second elongate lock panel of the two opposite second wing portions (30', 30'); (j) wherein after the two opposite first wing portions (30, 30) are folded into the folded position, the four elongate panel extensions are flippable 90 degrees about the transverse fold lines towards the two opposite second margins (32', 32') such that the elongate panel extensions are held within the two tubular frame sections (50', 50') formed after the two opposite second wing portions (30', 30') are folded into the folded position, and wherein the four tabs are inserted into and engaged with the four slits respectively at four corners of the picture frame, thereby locking the four tubular frame sections (50, 50') in the folded position.