I think that this is my cleanest formuals to show an image on a form and control the size. I presume from your question that each record will have its own logo, but I may have assumed incorrectly and you in fact want the same logo in every form.
var text FileType = Right(ToText([file attachment2]),".");
If(Contains("jpg, jpeg, png",$FileType),
"<img src=" & URLRoot() & "up/" & Dbid() & "/a/r" & [Record ID#] & "/e282/v0' width='75' >")
In the example above Field ID 282 has the file attachment.