Images composed of simple shapes, lines, and letters are often better expressed using vector graphics. These have a number of advantages such as making it easier for subsequent editors to edit them, enabling arbitrary scaling at high quality, and sharp high-resolution renderings for print versions. If you see an image like this, add {{Convert to SVG}} to it, which adds it to Category:Images that should use vector graphics. Certain JPEGs and PNGs are not suitable for transfer to the SVG format. These include heavily or artistically shaded images, or non-free images on other projects such as those of logos (conversion to a scalable format can represent a copyright violation). Images that have been uploaded at a high resolution and good quality are a lower priority for transfer to the SVG format. Efforts are better focused on converting lower quality, smaller images that will be substantially improved if redrawn as a SVG. Images which will appear the same but will require marginally less file space are a lower priority.

Raster images generated by libre (free) software programs, for which a source file is made available under a libre license, is also of lower priority. In fact, such images if the source file is provided should be left alone probably if the program does not provide SVG output, or else it may even be *harder* for subsequent editors to modify the image (the opposite of the stated goal above). It does help to request a feature for SVG output from the developers of such programs.

What to do: using vector graphics production software (see en:Comparison of vector graphics editors), remake the image. The original image can often be used as a template. Some notes:

If the image is derived from a third-party source, first check whether a vector version is available from that source. It is easier to convert a PDF into SVG than to remake the entire file.

Commons now supports uploads of STL files. Previously, contributors wishing to show a three-dimensional image would resort to uploading a video of the object rotating, or a still image of different views of the object. These are acceptable as ancillary files, but there are cases where the original 3D shape is the best way to convey the desired information. Therefore, there is a template listing files to have a source or derived 3D version uploaded: {{Convert to STL}}.

Although PNG is not a bad way of losslessly storing photographs, any thumbnail of a PNG appearing in an article will be in PNG format. The result is that these thumbnails have a large filesize, making them slow to download for many users (typically, about 10 times larger than JPEG thumbnails). Although ideally the software would be able to create JPEG thumbnails of PNG images, right now it can't. Additionally, sharpening is applied to JPEG thumbnails but not to PNG thumbnails, and sharpening is usually desirable for photographic thumbnails. See phab:T192744 for details on the design decision to not sharpen PNG thumbnails.

What to do: Create a JPEG version of the file and upload it; quality is not important when we do it this way as long as it looks good. Place {{PNG with JPEG version}} on the original PNG's page and {{JPEG version of PNG}} on the JPEG's page. This alerts people to refer to the JPEG version in articles, but to make edits to both versions, based on the PNG version.

Above a certain size, PNG, TIFF and GIF files are currently not provided with thumbnails by Commons' MediaWiki software (an error message is displayed). JPEG versions linked to the original file via {{Compressed version}} (although it does not need to be a compressed version) should be uploaded for preview purposes and used in Wikimedia websites. See COM:MAXTHUMB.

Partly because MediaWiki image pages scale down images by default, it's a common mistake to upload a scaled-down, lower-resolution image to Commons than the original image. This is unnecessary and undesirable; large images are necessary for use in print and other situations. If you see an image like this, add {{Thumbnail}} to it, which adds it to Category:Images uploaded at reduced resolution.

What to do: Upload or locate a larger resolution image of the same filetype. If the image is otherwise identical, tag it with {{duplicate|Image:example.jpg}} and give for the parameter the larger image. You or the person deleting it should use "check usage" to ensure that the small image is no longer used. See COM:Dupe for more information. If the larger image has differences, tag the old version with a {{Superseded}} tag instead.

EXCEPTION: For exceedingly large images, such as this 690 megapixel image, Commons' file viewers such as {{LargeImage}} can break, and the maximum thumbnail size Wikipedia will create is still far, far below the size of the image itself. In these cases, uploading a courtesy copy that can be viewed with the file viewers may be appropriate.

Example 1 (identical): Smaller version, larger version

Example 2 (differences): Smaller version, larger version

Wikimedia projects other than Commons, particularly those accepting non-free content, may prefer uploading of thumbnails for some purposes.

These images need to be rotated so they're upright.

A variety of sources can introduce unwanted overlaid patterns into an image, such as halftone patterns and text from the opposite page side bleeding through in scanned images and the presence of electromagnetic interference during image creation or processing. All of these (and also naturally occurring patterns, which should not be removed, such as fences and parts of other man-made objects) can cause moiré patterns to occur when resampling images without extra care taken to avoid them – something that is prone to happen in automatically generated image thumbnails for articles in particular.

What to do: Add {{CleanFFT}} to the image to include it in Category:Images containing regular noise. After that, ideally, find a better version of the picture that does not contain the noise. If this is not possible, in many cases you can clean up this type by editing the image in the frequency domain by doing either a Fourier or wavelet transform on the image. Such transformations can be done in both GIMP and Adobe Photoshop with the aid of suitable plugins. For more information on how to do this, see Commons:Cleaning up interference with Fourier analysis. If the size of the patterned noise is significantly smaller than the image details' then simply slightly blurring the image or using other general denoising methods can be very effective in eliminating them without any degradation to image quality, too.

Some images are not sufficient to clearly demonstrate the subject of the image; whether by being too blurry to digitally fix, being of small resolution and/or compression, not properly demonstrating the subject of the image, or being visually unappealing in another way. New versions with higher quality should be found and used instead. Low-quality images can be tagged with {{Low quality}} (or if applicable {{Blurry}}) to add them to Category:Images of low quality.

What to do: get a camera and take a better image, or try to find one under a free license. See, for example, 共享资源:自由媒体资源.