Paint by Numbers? Or perhaps, compute by pixels?
We're given an image that looks like this:
Based on the challenge name, this is a program written in the esolang Piet. Then, we can import the program into an online Piet IDE and try running it:
Based on the output, it looks like the given program is a flag checker. Because Piet is a stack-based language, we can assume that the flag will be on the stack; stepping through the instructions until the first output,
[0,125,116,115,49,116,114,52,95,110,52,95,51,109,48,99,51,98,95,51,118,52,104,95,100,108,117,48,104,115,95,49,123,109,116,112,80,4,4]
we get the flag:
ptm{1_sh0uld_h4v3_b3c0m3_4n_4rt1st}