Hi,
First of all, this is not an issue or a bug. And has nothing to do with our VM Template.
In the Virtuemart configuration there are fields for height and width for thumbnails. Those values are used while generating thumbnails to limit the height and width values. Lets assume you have set 200 for both height and width values.
Those values are to limit the size of thumbnails, they are not used to "fix" the resolution. Which is better.
Lets say, you have 2 product pictures;
One picture has 800x400 resolution
Other picture has 800x800 resolution.
After the thumbnails are generated, those pictures will have these thumbnails:
First picture will have thumbnail with 200x100
Other picture will have the thumbnail with 200x200
Got it? The first picture can't have a thumbnail of 200x200 because the result will look absurd. The thumbnail won't look good. It would look like it is stretched or contracted horizontally.
Therefore, you should be aware that your product picture must be in same resolution ratio. If you want good results....
So if you have 800x600 pictures, and also have 1600x1200 product pictures (since their height/width ratio is the same) you will get the same thumbnail resolution from both of those images.
I hope you got what i am saying.You can't get same thumbnails from 800x400 and 800x800 images. It just doesn't make any sense. You just can't do it.
Cheers.