Build 3.0.0.103 of xlsgen makes it possible to specify picture borders in XLS and XLSX files.

A Borders property appears in the IXlsPicture interface, which gives way to the usual suspects (width, color, style).

It goes like this (C++) :

xlsgen::IXlsPicturePtr pic1 = wksht->Pictures->Add(L"input\\aaadd.jpg");
pic1->TopCell = 2;
pic1->LeftColumn = 2;
pic1->Borders->Style = xlsgen::chartborderstyle_dashdot;
pic1->Borders->Color = xlsgen::colorRed;