create the imageI hope I made it all clear. I'll keep an eye for your release. Success!
before saving your image, make sure the color mod is at 8 bits (if it's not turn to 8 bit, but I advice you the image may loose some quality). finally, save as a .bmp file and use sprwiz (may be easily found by googling) to create a .spr file. now to use it in game all you need to do is name it properly(if you changed no .txt then name as the .spr you want to replace) and drop it in your valve(or mod name)/sprites folder.
- note its size in pixels must be the same as the original sprite you want to replace, as well as the picture(s) position(s). ** if it's not, then you will need to modify one or more .txt files located in half-life/valve(will vary if it's a mod)/sprites folder - but it's complicated to explain here.