From your words, there is the main requirement - to use it in background and to be it an excel file.
If you are an abap developer, this kind of scenario is soooooo regular and so misunderstod from the consultants and business people, that you can got grey hair from it.
Sap technology itself in general everyday words is a "proprietary" technology, which is capable of integrating with 3rd party components / software like office programs and many others. But being capable of creating export files of some kind that is accepted by the opening software does not mean that SAP replaces it's own mechanism of working with those files. When xmlx, docx etc. files came, those mean that openXML technology started to be used in office. When you are used to export tabular data to files, you usually export ASCII files containing fields separated either by tabs or by other characters (semicolon, comma...). Those can be easily read by excel, as it understands it. So you can save a file with excension .csv, rename it to .xls and open with excel and it will show the data you expect. Until saving it as .xls directly from excel it will remain still as tab-delimited or .csv data.
Your next requirement is to embedd a picture and formatting.. One needs to understand that those parts of .xlsx files are directly-proprietary to the format of openxml files (zipped couple of .xml files) and SAP - in - versions I am confronting with - is not able to work with those in general.
Go ahead with abap2xls(x) project, which unfortunately, as it seems, never gets any further than to a beta version. You can find it here abap2xlsx - ABAP Development - SCN Wik
Your every next question would still be more appreciated, if it was fore-represented by a search on the forum / google / other resources. You would find many more examples, when this whole approach is explained, even though not so detaily as by me in this post, as I drunk some vine right now.