If the problem is image quality :
The posted images are both of type JPEG. If this is the case, then every save in JPEG format will lose resolution. This format is lossy in the sense that every succeeding compression will cause some loss in image quality.
In addition, the two images are not of the same size, the second image actually larger than the first, so that pixel extrapolation will cause some further loss compared to the original.
If you wish for more accuracy, use a more evolved image editor than Paint, for example the free Paint.NET, and use a lossless format such as PNG (with or without compression).
If the problem is image size :
It is impossible that copy/paste changed the image size, so some other explanation is required.
The only explanations I can think of for the result of the above operation by the poster to be too small are:
- The screenshot was taken of the image when it was displayed as zoomed-out, so smaller.
- The paste was from a low-resolution image into a high-resolution one, which will make it look smaller.
In all cases, my advice is not to use screenshots for copying an image, but rather to export and import the image using the capabilities supplied by the products you are using.