That's ridiculous, OF COURSE if the image is the same size as your resolution/monitor/whatever else you want to call it, then you'll be OK.
No one asked if 1 + 1 = 1 + 1.
The question here is about scaling and the basic answer is:
Scaling up is a no no, it simply does not work with non-vector graphics as Pixelation or stretching will occur which degrades the quality of the image. Vector graphics will scale as they use mathmatical equations to represent the image, which scale. The ratio must remain the same, however.
As @sunpech rightly suggests, it would be best to pick a larger image to scale down, but this will only work if the image aspect is the same (such as 4:3 (standard) or 16:9 (widescreen) which are more commonly known than Brian's suggestion)).
Example scaling:
- 800 x 600 resolution (4:3 aspect)
will scale down perfectly well to 640
x 480 (4:3)
- 1920 x 1080 resolution (16:9 aspect)
will scale down perfectly well to
1280 x 720 (16:9)
- 2560 x 1600 resolution (16:10 aspect)
will scale down perfectly well to
1920 x 1200 (16:10)
a 16:10 won't scale down to a 16:9, while you may get away with it looking OK in some circumstances (1920x1200 to 1920x1080) for example, it is not a true scale down and will most likely have noticeable squashing of the image.