Translating images can be a nasty task if they contain text, the image background is complex or the original image is of poor quality or resolution. While best practices for translating and creating new images can be an expansive subject, there are fortunately many free software programs that assist the image translator with image creation and editing.
In the Free Software world, there are a few standard image editing software programs. When working with image formats such as jpeg, png, or gif, GIMP is the de facto editor. Notably only PNG is a free (libre) format, although gif is now free in most countries. If you work with vector graphics the most sophisticated Free Software tool is Inkscape. Both GIMP and Inkscape are available for Linux, Macintosh and Windows.
Using these tools, one has much flexibility for editing images however it is important to recognize the possibility of others localizing the image. Separating text from the image makes editing substantially easier. In many tools, text can be added as a separate layer, which means that the text can be edited and changed without affecting the rest of the image. However, layers can only be changed if you have the original source files that preserve them. Images in jpeg, gif, and png do not preserve layers. GIMP's source file is in XCF format. While those working in Photoshop will save their source files as PSD files. GIMP is able to import the native and proprietary format for PSD files using a plugin with CMYK colorspace support : http://www.blackfiveservices.co.uk/separate.shtml
In either case, these source files must somehow be made available to translators. Most files used in word processors, presentations, or in web pages are png, jpeg, or gif as these formats are best suited for display in a web browser. The file size of XCF and PSD files, on the other hand, are too large to put on the web and browsers do not render them. So a strategy is necessary to make the source files of images not only available, but also easily identifiable.
One strategy for making images easily translated is to use the open standard SVG, a vector graphic format. Text in an SVG image can be changed without changing the rest of the image because an SVG file is itself a text file. While SVG files can be edited in a text editor, there are SVG editors like the open source tool Inkscape that make it much easier. One of the main advantages of SVG is that the image file itself is the source file. However, SVG as a format is not widely supported by many applications, and most importantly not all browsers will display SVG. Therefore, many times it's necessary to export SVG to png (or another supported format) to use it in a webpage and are left again with the problem of keeping the source SVG file somewhere available for translators.