After downloading an image, i found that it is a .png format, therefore i tried a tool like zstego for extracting something inside and boom! it worked as follows:
┌─[alexius@alexius-hpprobook4430s]─[~/Downloads]└──╼ $zsteg -a pico.flag.png b1,rgb,lsb,xy       .. text: "picoCTF{7h3r3_15_n0_5p00n_4706df81}$t3g0"b1,abgr,lsb,xy      .. text: "E2A5q4E%uSA"b2,b,lsb,xy         .. text: "AAPAAQTAAA"b2,b,msb,xy         .. text: "HWUUUUUU"b3,r,lsb,xy         .. file: gfxboot compiled html help fileb3,b,msb,xy         .. file: StarOffice Gallery theme @\002 H\200\004H\002\004H\200$H\022\004H\200\004\010, 0 objectsb4,r,lsb,xy         .. file: Targa image data (16-273) 65536 x 4097 x 1 +4352 +4369 - 1-bit alpha - right "\021\020\001\001\021\021\001\001\021\021\001"b4,g,lsb,xy         .. file: 0420 Alliant virtual executable not strippedb4,b,lsb,xy         .. file: Targa image data - Map 272 x 17 x 16 +257 +272 - 1-bit alpha "\020\001\021\001\021\020\020\001\020\001\020\001"b4,bgr,lsb,xy       .. file: Targa image data - Map 273 x 272 x 16 +1 +4113 - 1-bit alpha "\020\001\001\001"b4,rgba,lsb,xy      .. file: Novell LANalyzer capture fileb4,rgba,msb,xy      .. file: Applesoft BASIC program data, first line number 8b4,abgr,lsb,xy      .. file: Novell LANalyzer capture fileb6,r,msb,xy         .. file: MacBinary, busy, bozo, ID 0x800, protected 0x2, char. code 0x40, total length 34078852, 2nd header length 2, Sat Mar 16 09:26:08 2075 INVALID date, modified Sun Mar 25 23:08:00 2040, creator '0\01', type 'C\02', 8388672 bytes "\200 \010\002" , at 0x8000c0 136347648 bytes resourceb6,g,lsb,xy         .. file: StarOffice Gallery theme , 1074791425 objects, 1st \001b6,g,msb,xy         .. file: tar archive (old), type '@'  , uid  \200, gid \002\01, seconds @\010 \200, linkname \010b6,b,msb,xy         .. file: tar archive (old), type '@'  , uid  \200, gid \002\01, seconds @\010 \200, linkname \010b6,rgb,lsb,xy       .. file: GLS_BINARY_MSB_FIRSTb6,rgb,msb,xy       .. file: Applesoft BASIC program data, first line number 130b6,bgr,lsb,xy       .. file: GLS_BINARY_LSB_FIRSTb6,abgr,msb,xy      .. file: Applesoft BASIC program data, first line number 2b8,bgr,lsb,xy       .. file: PDP-11 UNIX/RT ldpb8,rgba,lsb,xy      .. file: Targa image data - Map (256-0) 257 x 65536 x 1b8,abgr,lsb,xy      .. file: Windows Precompiled iNF, version 1.0, InfStyle 1, flags 0x1000000, at 0x1000100, WinDirPath "",, LanguageID 101, at 0x1000100, at 0x1000000b1,abgr,lsb,xy,prime.. text: "Gu!U1`Q[9"b2,g,lsb,xy,prime   .. file: 0421 Alliant compact executableb2,bgr,msb,xy,prime .. file: MacBinary, Wed Jan 25 18:49:20 2023, modified Mon Feb  6 09:28:16 2040 "*\240(\250\252\210\200\242\210\202", at 0x80 6354557 bytes resourceb3,b,msb,xy,prime   .. file: MacBinary, char. code 0x4, Mon Feb  6 09:28:16 2040 INVALID date, modified Mon Feb  6 09:28:16 2040 "\222$@\002\004AI%\001"b3,bgr,lsb,xy,prime .. file: Intel ia64 COFF object file, no line number info, not stripped, 9288 sections, symbol offset=0x41902449, 67703296 symbols, optional header size 274b3,rgba,lsb,xy,prime.. file: MacBinary, Mon Feb  6 09:28:16 2040 INVALID date, modified Mon Feb  6 09:28:16 2040 "@ "b4,r,lsb,xy,prime   .. file: Novell LANalyzer capture fileb4,g,lsb,xy,prime   .. file: PDP-11 UNIX/RT ldpb4,rgb,lsb,xy,prime .. file: Targa image data (4112-4113) 4369 x 257 x 1 +1 +4369b4,abgr,lsb,xy,prime.. file: TeX font metric data (\020)b5,g,msb,xy,prime   .. file: Intel ia64 COFF object file, not stripped, 8 sections, symbol offset=0x100400, 142605824 symbols, optional header size 64b5,b,lsb,xy,prime   .. file: Intel ia64 COFF object file, not stripped, 1040 sections, symbol offset=0x2080084, 1749723392 symbols, optional header size 66b6,r,lsb,xy,prime   .. file: MacBinary, Fri Jan  8 23:33:04 2066 INVALID date, modified Mon Feb  6 09:28:16 2040 "@\004\020\001\004\020\001\004\020A", at 0x80 344844 bytes resourceb6,g,msb,xy,prime   .. file: Applesoft BASIC program data, first line number 128b6,rgb,lsb,xy,prime .. file: Targa image data - Map 4096 x 1024 x 16 +1089 +256 - 1-bit alpha - interleaveb6,bgr,lsb,xy,prime .. file: X11 SNF font data, MSB firstb6,rgba,lsb,xy,prime.. file: X11 SNF font data, MSB firstb7,b,lsb,xy,prime   .. file: Targa image data - RLE 64 x 2 x 8 +4 +8192b8,r,lsb,xy,prime   .. file: raw G3 (Group 3) FAX, byte-paddedb8,b,lsb,xy,prime   .. file: Targa image data - Map 257 x 65536 x 1 +257b1,bgr,lsb,yx       .. <wbStego size=192, ext="\x00\x00\x00", data="\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"..., even=false>b2,b,msb,yx         .. text: "eUUUUUi;"b4,r,lsb,yx         .. text: "_CD#C42DS"b4,g,lsb,yx         .. file: TIM image, Pixel at (0,0) Size=0x0b4,b,lsb,yx         .. file: TIM image, Pixel at (0,0) Size=0x0b4,b,msb,yx         .. text: "UYUUUUUUUUUU"b4,rgb,lsb,yx       .. file: Novell LANalyzer capture fileb4,rgba,lsb,yx      .. file: Novell LANalyzer capture fileb4,abgr,lsb,yx      .. file: Novell LANalyzer capture fileb5,g,msb,yx         .. file: TIM image, Pixel at (0,0) Size=0x0b5,b,msb,yx         .. file: TIM image, Pixel at (0,0) Size=0x0b6,rgb,lsb,yx       .. file: MacBinary, Mon Feb  6 09:28:16 2040 INVALID date, modified Mon Feb  6 09:28:16 2040 "@"b6,rgb,msb,yx       .. file: Applesoft BASIC program data, first line number 2b6,rgba,lsb,yx      .. file: MacBinary, Mon Feb  6 09:28:16 2040 INVALID date, modified Mon Feb  6 09:28:16 2040 "@"b6,rgba,msb,yx      .. file: Applesoft BASIC program data, first line number 2b6,abgr,lsb,yx      .. file: MacBinary, Mon Feb  6 09:28:16 2040 INVALID date, modified Mon Feb  6 09:28:16 2040 "@"b6,abgr,msb,yx      .. file: Applesoft BASIC program data, first line number 2b8,b,msb,yx         .. text: ["S" repeated 9 times]b8,rgb,lsb,yx       .. file: Windows Precompiled iNF, version 1.0, InfStyle 1, at 0x0 "", WinDirPath "", LanguageID 0b8,bgr,lsb,yx       .. file: PDP-11 UNIX/RT ldpb1,b,lsb,yx,prime   .. file: Apple HFS/HFS+ resource forkb2,b,msb,yx,prime   .. text: "PUUUU@UUUU"b4,r,lsb,yx,prime   .. text: ["3" repeated 8 times]b4,b,msb,yx,prime   .. text: ["U" repeated 8 times]b8,b,msb,yx,prime   .. text: ["S" repeated 8 times]b4,r,lsb,XY         .. text: "\ncCTDDDC322C5"b8,a,msb,YX         .. text: "8QQQQQQQQQQQ:"b1,r,lsb,Xy         .. text: "q}$c~!}}?0~V="b2,b,lsb,Xy         .. text: "PPEQPPAPPQ"b4,r,lsb,Xy         .. text: "C35#\"2#\"#2Bq"b8,a,msb,yX         .. text: ":QQQQQQQQQQQ8"b1,r,lsb,yX,prime   .. file: QL OS dump data,b1,r,msb,yX,prime   .. file: Apple DiskCopy 4.2 image , 67143680 bytes, 0xc0130060 tag size, GCR CLV ssdd (400k), 0xf8 formatb1,a,msb,yX,prime   .. file: Apple DiskCopy 4.2 image , 67143680 bytes, 0x80010060 tag size, GCR CLV ssdd (400k), 0xf8 formatb2,rgba,lsb,xY      .. text: "!\"\"! #6e"b4,r,lsb,xY         .. text: "3B233DDDDSCj"b4,abgr,lsb,xY      .. text: "$P$@$0$!4"b5,abgr,lsb,xY      .. text: "Dt$GBD,$JBD"b5,abgr,msb,xY      .. text: "B\"4$RB\"8$"b8,r,msb,xY         .. text: ["#" repeated 8 times]b8,g,msb,xY         .. text: "!(HHHHHH"b8,b,lsb,xY         .. text: "1000000110122U"b5,rgb,msb,xY,prime .. text: "@@a I\n8%"b2,b,msb,Yx         .. text: "iUUUUUY?"b4,r,lsb,Yx         .. text: "_5D#C42D4"b4,b,msb,Yx         .. text: "YUUUUUUUUUU"b8,b,msb,Yx         .. text: ["S" repeated 9 times]b1,b,lsb,Yx,prime   .. file: dBase IV DBT, blocks size 0, block length 2048, next free block index 196608, next free block 0, next used block 0b1,b,msb,Yx,prime   .. file: dBase IV DBT, blocks size 0, block length 4096, next free block index 12582912, next free block 0, next used block 0b2,b,msb,Yx,prime   .. text: "TUUU!pUUU5PUU"b4,r,lsb,Yx,prime   .. text: ["3" repeated 8 times]b4,b,msb,Yx,prime   .. text: "PUUUUUUUU"b8,b,msb,Yx,prime   .. text: ["S" repeated 8 times]
>>since the answer has $st3g0 at the end therefore the flag will be: picoCTF{7h3r3_15_n0_5p00n_4706df81}>>hint:; tools like steghide will NOT work for .png files