What can be the reason that an image (.jpg) is inserted as PNG using drag & drop to the Artwork field or using the Update Image window?
When I did this a month ago a .jpg image was inserted as JPG and not as PNG.
Certainly when you Copy something to the clipboard and then try and Paste the item from the clipboard into Jaikoz the Data Flavors offered to Jaikoz may not include the original image/file but just a presentation of it so that you no longer have the original bytedata. In these cases Jaikoz has to rewrite the image in a format of its choosing and I default to PNG as this is more reliable than JPG.
I suspect we have a similar problem with drag 'n' drop. Nothing has changed in the Jaikoz code except for moving the underlying Java version to Java 8 which may have had an effect, but probably more relevant is where you are dragging from ?
I found out that if an image is larger than Local Correct -> Artwork Correct -> Resize artwork if dimensions lager than (pixels): than Jaikoz rewrites the image in a format of its choosing and the default is PNG (as this is more reliable than JPG).
I would prefer a switch, where I can select PNG or JPG