You cannot convert GIF pictures (.gif) to Excel spreadsheets (.xls). However, you can import pictures (including GIF format) to one of the list in the spreadsheet as object. This can be done through the import Object function in MS Excel or similar spreadsheet program.
Some other programs may also claim that they offer means to convert gif to xls, but they almost always just create empty sheet with the picture on one the first list, that is, if the offered gif to xls conversion works at all.Open GIF file Open XLS file
An universal picture and document converter
A graphical data digitizing software