Hi bulldogs,
Thanks for contributing to our forum. We do not offer any functionality that could be used to increase the dimensions of the Gallery images in your active listings in bulk so, unfortunately, updating the Gallery Images in your active listings to be at least 500 px on the longest side will require revising each listing individually as you have described.
If you have images in your Auctiva account which are less then 500 px on the longest side and you would like to enlarge them to ensure you do not encounter issues when you use them in the future, you can potentially resize them using the “Edit” option on your Image Management page.
However, it is only possible to resize one image at a time from the Image Management page as well and increasing the dimensions of an image (as opposed to taking a new, larger version) is likely to have an adverse impact on the quality of the image.
I am not sure it would be feasible to create a tool that could be used to automatically increase the dimensions of your active Gallery images to comply with this new policy, but we will consider your comments in this regard when planning future updates to our site.
-Mike