There's really no way to restore the default; once it is overwritten it is gone. You can use ITK to install a replacement image. You could, for example, grab and use one of the Intel logo images that is available on the internet (see Google Images or Wikipedia, for example)...
Answering your other question, download and install the latest version of ITK (v126.96.36.1995).
Within ITK, if you attempt to edit a BIO file that uses the older format (like that for DQ57TM), it will automatically switch to the old version of ITK.
In the old version of ITK, you click on Flex Modules and then right click on the logo entry (usually DPSD Logo) and select Edit Module. In the Customize BIOS Splash Screen dialog, click on File then Open Graphics File and then use the file selection dialog to select the file you want. Next, click on File then Update BIOS File to save the file and then on File and Exit to return to the ITK GUI. You can then click on Continue and then Finish to have the updated BIO and EBU .EXE files generated.
Hope this helps,