'change IMGS to imgs, and dim imgs as JQueryElement ,id should in lower-case for b4j;
<img border="0" src="upimg.png" id="imgs" style="display:none"/>
Private imgs as JQueryElement
Sub Timer1_Tick
.........
temperature.SetHtml(t)
If Main.upimg.Visible Then
imgs.SetCSS("display", "none")
Else
imgs.SetCSS("display", "block")
End If
........