how to use onmouseover function instead of selectedindexchanged event in gridview asp.net?

I don't see why not. Is your Datalist databound? I mostly use gridviews, but I assume same concept. If there is a row or item databound event you should be able to grab the control inside the datalist. It should call this for each record, you'll have to check if its a header row or datarow usually by checking the "e" event argument. Then do an piccontrol = e.findcontrol("picturecontrolname"). If it finds it, then put piccontrol.attributes.add("onmouseover","javascriptfunction()"). This is very rudimentary code and not exact syntax but concepts are here. Hope it helps.