Origin Version 7, 7.5 We want to add an insert (TIFF bitmap ) to a Origin plot with a couple of layers. The TIFF picture is sometimes distorted (with a wrong aspect ratio). Distortion seems to occur when the Origin page has been rotatated. You can reproduce this by exporting any origin graph to tiff file and importing it back to the same page (and resizing it keeping the aspec ratio). If you now rotate the page, the aspect ratio of the tiff image changes. The TIFF object properties (attach to page, layer or layer & page does not seem to have an effect (actually, I guess the object should be floating (attach to none?))
Once you import an image back to origin, you can right click the image object and select "properties" to open the "object properties" dialog. In the "Dimensions" tab, there is a check box "Keep aspect ratio", check it and Ok. Then you can resize the graph by keeping the aspect ratio and it will not change when you rotate the page.