Do you have received any feedback that we can't copy and paste the photo directly to excel online?
However paste the photo to Google Spreadsheet is working well.
@Wee Teck Tan Google Sheets and Excel online are different products and their functionality range is not the same. Currently it is not possible to add an image to Excel online by pasting. If you're passionate about this you may want to suggest this as a feature at https://excel.uservoice.com/forums/274580-excel-online