GIMP (GNU Image Manipulation Program) is the free alternative to Photoshop, and it is genuinely capable. It handles layers, masks, filters, colour correction, retouching, and batch processing. It supports JPEG, PNG, TIFF, PSD, and its own native XCF format. It runs on Windows, Mac, and Linux.
The honest assessment: GIMP can do most of what Photoshop does for image editing and texture work, but it does not always do it as smoothly. The interface has improved over the years, but it still has its own logic that takes some adjusting to if you are coming from Adobe. Non-destructive editing is more limited, and some of the more advanced features (like content-aware fill) are either absent or handled through third-party plugins.
Where GIMP earns its place is accessibility. It is completely free, it does not require a subscription, and it is powerful enough for serious texture work, photo editing, and digital painting. For Second Life creators working on textures, skins, or promotional graphics, GIMP is a solid choice, particularly if you are not ready to commit to an Adobe subscription. The plugin ecosystem (particularly Script-Fu and Python-Fu) extends its capabilities considerably if you are willing to dig into it.
If you already have Photoshop and know it well, there is no urgent reason to switch. If you do not, and you need a capable image editor without the monthly cost, GIMP does the job.
Sources and further reading
GIMP Official Site
https://www.gimp.org/
GIMP Downloads
https://www.gimp.org/downloads/
GIMP Features
https://www.gimp.org/features/
GIMP Documentation
https://www.gimp.org/docs/
GIMP User Manual
https://docs.gimp.org/
GIMP User Manual, Introduction
https://docs.gimp.org/3.0/en/introduction.html
GIMP User Manual, Layers
https://docs.gimp.org/3.0/en/gimp-image-combining.html
GIMP User Manual, Layer Masks
https://docs.gimp.org/3.0/en/gimp-layer-mask.html
GIMP User Manual, Filters
https://docs.gimp.org/3.0/en/filters.html
GIMP User Manual, Colour Tools
https://docs.gimp.org/3.0/en/gimp-tools-color.html
GIMP User Manual, Retouching
https://docs.gimp.org/3.0/en/gimp-imaging-photos.html
GIMP User Manual, File Formats
https://docs.gimp.org/3.0/en/gimp-images-out.html
GIMP Developer Documentation, Image File Formats
https://developer.gimp.org/core/standards/images/
GIMP Developer Documentation, Script-Fu Tools
https://developer.gimp.org/resource/script-fu/scriptfu-tools/
GIMP Plug-In Development
https://developer.gimp.org/resource/writing-a-plug-in/
GIMP Tutorials
https://www.gimp.org/tutorials/
GIMP Frequently Asked Questions
https://www.gimp.org/docs/userfaq.html
GIMP Release Notes
https://www.gimp.org/release-notes/
GIMP 3.0 Release Notes
https://www.gimp.org/release-notes/gimp-3.0.html
GIMP Foundation / About
https://www.gimp.org/about/
GNU Project, GIMP
https://www.gnu.org/software/gimp/
Second Life Wiki, Textures
https://wiki.secondlife.com/wiki/Texture
Second Life Wiki, Clothing Tutorials
https://wiki.secondlife.com/wiki/Clothing_Tutorials
Second Life Knowledge Base, Uploading assets
https://lindenlab.freshdesk.com/support/solutions/articles/31000134277-uploading-assets
Second Life Marketplace
https://marketplace.secondlife.com/