Windows displays file size incorrectly. The image reported to be 4,51 GB in size is actually 4,51 GiB (gibibytes), which is approximately 4,82 GB.
In 'SI units', we use a factor 1000 for prefixes, because that's a round number in the decimal system. 1000 equals 1 kilo, 1000 kilo equals 1 mega and so on. In the binary system, the closest round number is 1024. However confusing to someone not very familiar with binary numbers, 1024 was often used as a base for the sake of simplicity. To signify the difference between a normal and a 'binary' kilobyte, a common convention was to use a capital K for the latter (i.e. 1 KB = 1024 B = 1,024 kB).
As symbols for the prefixes mega-, giga- etc. were already capitalised, an alternate scheme was proposed that included an 'i' after the symbol: 1 KiB = 1024 B, 1 MiB = 1024 KiB... Unfortunately, the convention of the so-called kibibyte was far less universally adopted, resulting in possible ambiguity. Often, numbers a presented with SI units, whether 1000 or 1024 has been used as a base internally. As a result, a hard drive manufacturer's gigabyte can be roughly 7% smaller than your operating system's gigabyte.
In your case, the image really is too large to fit on the dvd, but both sizes are displayed using different conventions.