Adding a picture for Doom maps

I hope to use some of my favourite pictures for some wall in Doom maps designed by me, like this:



How can I do it? Is it something related to XWE or something?

SLADE would be a better choice.

Regardless, what's the intended port? If ZDoom, you could save it as a PNG and put it between TX_START/_END (or P_START/_END and a TEXTURES lump defining it as a high-resolution image, I suppose). If something using the more traditional Doom texture setup, you'd put it between P_START/_END, right-click and convert it to Doom Texture Format, and select the Doom palette for the palette it should map to. You can also save it to the Doom palette ahead of time in an external program, which might do a better job at the conversion than SLADE would (Photoshop would give you dithering options, for instance).