If it's a PDF you probably just need to make sure you have selected "Actual size" and not "Fit" or "Shrink oversized pages" which will change the scaling.
If it's a raster image (JPG, PNG, etc), you need to figure out the appropriate scaling and then specify it for the program. I mainly use PaintShop Pro, in which the print dialog lets you specify the printed width, height, and/or scale. If you don't know the scale, in PSP when you draw a selection box around something, it shows the box's dimensions (in pixels) in the lower right corner, so find something you know the size of (e.g. if there are grid squares that's an easy reference) and draw a box around it. The specifics will differ in other programs though.