How to manage the image options in PrestaShop 1.5-1.6
To manage image types/sizes, the options for image quality and for pictures uploaded by customers, and to regenerate uploaded images, go to Preferences menu>Images sub-menu in the admin panel of your PrestaShop.
Manage Image Types
At the top of the page that opens when you go to Preferences menu>Images sub-menu you'll see a table with the different image types. Each image type has its width and height dimensions and is associated with one or more content types (e.g. products, categories, manufacturers, etc.). All this is shown in the table. When you upload an image for some content (e.g. a product), in addition to the original image resized copies will be created for each of the image types that's enabled for the particular content type. For example, if you upload a product image, additional copies will be created using the dimensions of the image types small_default, medium_default, large_default, etc.
To edit the options of an image type, simply click on its Edit button in the table. To add a new image type, click on the Add new image type button that's in the top right corner of the page (in PrestaShop 1.5 the button is labeled Add new). The form for adding/editing image types contains options for specifying a name for the image type, for the width and height dimensions (in pixels), and also options for enabling/disabling the image type so that it's used or not with the different content types.
To delete image types, in the table that lists the existing image types click on the arrow that's next to the Edit button for the particular image type, and then click on the Delete button. In PrestaShop 1.5 the Delete button is in the last column of the table.
Options for Image Quality and for Images Uploaded by Customers
When you go to Preferences menu>Images sub-menu in the back office under the table with the image types there are some options for the image quality and for images uploaded by customers. From the Image Quality option you can select the image format that's used. By default, JPEG/JPG is used. If you want to, you can change it to PNG. We recommend that you leave it to the JPEG format. Note that whatever format you select, you are allowed to upload JPEG/JPG, PNG or GIF images. PrestaShop will automatically convert the image into the default format. Under the option for the format there are a couple of options for the image quality: JPEG quality and PNG quality. The JPEG quality can be set from 0 to 100 (0 is the worst quality and 100 the best). The PNG quality can be set from 0 to 9 (9 is the worst quality and 0 the best).
Below the options for image format and quality there are some settings related to images uploaded by customers. Customers can upload images for products for which you've enabled customizations. From the option Maximum size of product pictures you can set the maximum allowed size. If the picture is bigger the customer won't be allowed to upload it. The option is in bytes; the default allowed size equals around 8 megabytes. When a customer uploads a picture the original picture will be uploaded on your hosting account and a resized copy will also be created. From the options Product picture width and Product picture height you can set the dimensions of this resized copy.
If you make any changes don't forget to click on the Save button.
At the bottom of the page with all the image settings there's a section for regenerating images. It's labeled Regenerate Thumbnails. If you make any changes to the options of existing image types and you want these changes to be reflected on the images that are already uploaded, you have to regenerate the images. You also have to do it after you add new image types. From the drop-down menu Select an image you can choose whether to regenerate the images for all content types or only for a specific one. Under the drop-down menu there's an option from which you can select whether to erase or not the old images. After that click on the button Regenerate thumbnails.
For screenshots and for more details on all the image options check out the tutorial on how to configure and manage the image settings in PrestaShop 1.5 and 1.6.