ERROR: Fatal error: Call to undefined function imagecreatefromjpeg() or imagecreatefromgif() or imagecreatefrompng()

ERROR: Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 3264 bytes)

PROBLEM: Only the code {becssg}folder{/becssg*} is shown - usage in module position

ERROR: Fatal error: Call to undefined function imagecreatefromjpeg() or imagecreatefromgif() or imagecreatefrompng()

If you get this error when trying to open a page that contains a gallery, this means that the GD library, an extension for PHP is not activated at all or does not support the used image file type.
The GD Library, short GD or GDlib, is a program library to dynamically create and manipulate graphics and one of the most widespread extensions of PHP. The CSS Gallery uses this extension to scale the main images and to create the thumbnails.
To check if the GDlib is activated on your server go to the Joomla! administration interface and open Help > System Info >PHP-Information. On this page search for "gd". In the best case you will find a chapter with the following or similar content:

gd

• GD Support enabled
• GD Version bundled (2.0.34 compatible)
• FreeType Support enabled
• FreeType Linkage with freetype
• FreeType Version 2.1.9
• T1Lib Support enabled
• GIF Read Support enabled
• GIF Create Support enabled
• JPG Support enabled
• PNG Support enabled
• WBMP Support enabled
• XBM Support enabled

The first line shows, that the extension is enabled, the second line holds the installed version. The followup lines hold information about available functionality and supported file types. For the CSS Gallery the file types GIF, JPG and PNG are of importance.
If the GDlib is not activated or these file formats are not supported, you should (on your local test environment) activate it or (on the web server) ask your hoster if it is possible to add this feature. Without the GDlib the CSS Gallery cannot be used.

ERROR: Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 3264 bytes)

If you get this error (amount of bytes will vary) when trying to open a page that contains a gallery, the amount of memory PHP needs to create the scaled main images or the thumbnails exceeds the set maximum amount of memory a PHP script is allowed to use.
One possible solution would be to increase this amount (on your local test environment) or (on the web server) to ask your hoster if it is possible to enhance your account but - with a probability of 99% - the simple solution is: Smaller images!

In many cases images get uploaded far to large for web use. A common Joomla! template offers for a gallery in the context of the main content from 600 up to 800 pixel of width at the maximum. Images of this size can be displayed at excellent quality with - depending on the image - 50 up to 100 kilobyte. If you upload your images as they are saved from your digicam, they often come with dimensions up to 3000 or 4000 pixel of width and 3 or 4 megabyte of size.
The disadvantages of such large images are obviously: The upload takes a long time, you need a lot of space on your server and - important - scarcely any visitor is willing to wait for an image of 3 or 4 MB to load. Furthermore scaling an image offline with an appropriate program (e.g.: GIMP) gives you much better results than leaving it up to the visitors browser.

In the best case you scale your images offline to a format that exactly matches the size you are going to display them on your page (if you already fine tuned the gallery) or is a little above this size (above because browsers are still worse in up scaling images than they are in down scaling them).

By the way - doing so, the error disappears too.

PROBLEM: Only the code {becssg}folder{/becssg*} is shown - usage in module position

If the frontend shows the code - {becssg}folder{/becssg*} (without asterisk) - instead of the gallery, the first thing to do is to check if the plugin is activated. If it is and the problem persists, in most cases you are trying to display the gallery on a module position instead of the context of the main content.
Not all extensions, that offer to display custom content on a module position, are supporting the whole functionality of the Joomla! framework and with it the functions the plugin needs to work properly.
Up till now two extensions are reported to offer the needed functionality:

One is the module "Module: Content with Plugins", listed at extensions.joomla.org under "News Display" > "Articles Embed".
The other is the module "Plugin in Module", listed at extensions.joomla.org under "Core Enhancements" > "Embed & Include".

If you use this extensions, please post a rating and a review at extensions.joomla.org. Furthermore I appreciate everyone, supporting me with a link back to www.bretteleben.de on his/her website. The extension itself does not produce any hidden links, eastereggs or whatever.